--- 1/draft-ietf-httpbis-rfc6265bis-07.txt 2021-06-02 14:13:11.315499824 -0700 +++ 2/draft-ietf-httpbis-rfc6265bis-08.txt 2021-06-02 14:13:11.427502653 -0700 @@ -1,19 +1,23 @@ -HTTP M. West, Ed. -Internet-Draft Google, Inc -Obsoletes: 6265 (if approved) J. Wilander, Ed. -Intended status: Standards Track Apple, Inc -Expires: 10 June 2021 7 December 2020 +HTTP L. Chen, Ed. +Internet-Draft Google LLC +Obsoletes: 6265 (if approved) S. Englehardt, Ed. +Intended status: Standards Track Mozilla +Expires: 4 December 2021 M. West, Ed. + Google LLC + J. Wilander, Ed. + Apple, Inc + 2 June 2021 Cookies: HTTP State Management Mechanism - draft-ietf-httpbis-rfc6265bis-07 + draft-ietf-httpbis-rfc6265bis-08 Abstract This document defines the HTTP Cookie and Set-Cookie header fields. These header fields can be used by HTTP servers to store state (called cookies) at HTTP user agents, letting the servers maintain a stateful session over the mostly stateless HTTP protocol. Although cookies have many historical infelicities that degrade their security and privacy, the Cookie and Set-Cookie header fields are widely used on the Internet. This document obsoletes RFC 6265. @@ -38,25 +42,26 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on 10 June 2021. + + This Internet-Draft will expire on 4 December 2021. Copyright Notice - Copyright (c) 2020 IETF Trust and the persons identified as the + Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. @@ -74,98 +79,106 @@ than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Conformance Criteria . . . . . . . . . . . . . . . . . . 5 2.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5 2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7 + 3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Server Requirements . . . . . . . . . . . . . . . . . . . . . 9 4.1. Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . 9 4.1.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . 9 4.1.2. Semantics (Non-Normative) . . . . . . . . . . . . . . 11 4.1.3. Cookie Name Prefixes . . . . . . . . . . . . . . . . 14 4.2. Cookie . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . 16 4.2.2. Semantics . . . . . . . . . . . . . . . . . . . . . . 16 5. User Agent Requirements . . . . . . . . . . . . . . . . . . . 16 5.1. Subcomponent Algorithms . . . . . . . . . . . . . . . . . 17 5.1.1. Dates . . . . . . . . . . . . . . . . . . . . . . . . 17 5.1.2. Canonicalized Host Names . . . . . . . . . . . . . . 18 5.1.3. Domain Matching . . . . . . . . . . . . . . . . . . . 19 5.1.4. Paths and Path-Match . . . . . . . . . . . . . . . . 19 5.2. "Same-site" and "cross-site" Requests . . . . . . . . . . 20 5.2.1. Document-based requests . . . . . . . . . . . . . . . 21 5.2.2. Worker-based requests . . . . . . . . . . . . . . . . 22 - 5.3. The Set-Cookie Header . . . . . . . . . . . . . . . . . . 23 - 5.3.1. The Expires Attribute . . . . . . . . . . . . . . . . 25 - 5.3.2. The Max-Age Attribute . . . . . . . . . . . . . . . . 25 - 5.3.3. The Domain Attribute . . . . . . . . . . . . . . . . 26 - 5.3.4. The Path Attribute . . . . . . . . . . . . . . . . . 26 - 5.3.5. The Secure Attribute . . . . . . . . . . . . . . . . 27 - 5.3.6. The HttpOnly Attribute . . . . . . . . . . . . . . . 27 - 5.3.7. The SameSite Attribute . . . . . . . . . . . . . . . 27 - 5.4. Storage Model . . . . . . . . . . . . . . . . . . . . . . 28 - 5.5. The Cookie Header . . . . . . . . . . . . . . . . . . . . 33 - 6. Implementation Considerations . . . . . . . . . . . . . . . . 36 - 6.1. Limits . . . . . . . . . . . . . . . . . . . . . . . . . 36 - 6.2. Application Programming Interfaces . . . . . . . . . . . 36 - 6.3. IDNA Dependency and Migration . . . . . . . . . . . . . . 36 - 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 37 - 7.1. Third-Party Cookies . . . . . . . . . . . . . . . . . . . 37 - 7.2. User Controls . . . . . . . . . . . . . . . . . . . . . . 38 - 7.3. Expiration Dates . . . . . . . . . . . . . . . . . . . . 38 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 38 - 8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 38 - 8.2. Ambient Authority . . . . . . . . . . . . . . . . . . . . 39 - 8.3. Clear Text . . . . . . . . . . . . . . . . . . . . . . . 39 - 8.4. Session Identifiers . . . . . . . . . . . . . . . . . . . 40 - 8.5. Weak Confidentiality . . . . . . . . . . . . . . . . . . 41 - 8.6. Weak Integrity . . . . . . . . . . . . . . . . . . . . . 41 - 8.7. Reliance on DNS . . . . . . . . . . . . . . . . . . . . . 42 - 8.8. SameSite Cookies . . . . . . . . . . . . . . . . . . . . 42 - 8.8.1. Defense in depth . . . . . . . . . . . . . . . . . . 43 - 8.8.2. Top-level Navigations . . . . . . . . . . . . . . . . 43 - 8.8.3. Mashups and Widgets . . . . . . . . . . . . . . . . . 44 - 8.8.4. Server-controlled . . . . . . . . . . . . . . . . . . 44 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 - 9.1. Cookie . . . . . . . . . . . . . . . . . . . . . . . . . 44 - 9.2. Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . 44 - 9.3. Cookie Attribute Registry . . . . . . . . . . . . . . . . 45 - 9.3.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 45 - 9.3.2. Registration . . . . . . . . . . . . . . . . . . . . 45 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 46 - 10.2. Informative References . . . . . . . . . . . . . . . . . 48 - Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . 49 - A.1. draft-ietf-httpbis-rfc6265bis-00 . . . . . . . . . . . . 49 - A.2. draft-ietf-httpbis-rfc6265bis-01 . . . . . . . . . . . . 50 - A.3. draft-ietf-httpbis-rfc6265bis-02 . . . . . . . . . . . . 50 - A.4. draft-ietf-httpbis-rfc6265bis-03 . . . . . . . . . . . . 51 - A.5. draft-ietf-httpbis-rfc6265bis-04 . . . . . . . . . . . . 51 - A.6. draft-ietf-httpbis-rfc6265bis-05 . . . . . . . . . . . . 52 - A.7. draft-ietf-httpbis-rfc6265bis-06 . . . . . . . . . . . . 52 - A.8. draft-ietf-httpbis-rfc6265bis-07 . . . . . . . . . . . . 52 - Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 53 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 + 5.3. Ignoring Set-Cookie Header Fields . . . . . . . . . . . . 23 + 5.4. The Set-Cookie Header Field . . . . . . . . . . . . . . . 23 + 5.4.1. The Expires Attribute . . . . . . . . . . . . . . . . 26 + 5.4.2. The Max-Age Attribute . . . . . . . . . . . . . . . . 26 + 5.4.3. The Domain Attribute . . . . . . . . . . . . . . . . 26 + 5.4.4. The Path Attribute . . . . . . . . . . . . . . . . . 27 + 5.4.5. The Secure Attribute . . . . . . . . . . . . . . . . 27 + 5.4.6. The HttpOnly Attribute . . . . . . . . . . . . . . . 27 + 5.4.7. The SameSite Attribute . . . . . . . . . . . . . . . 28 + 5.5. Storage Model . . . . . . . . . . . . . . . . . . . . . . 30 + 5.6. Retrieval Model . . . . . . . . . . . . . . . . . . . . . 35 + 5.6.1. The Cookie Header Field . . . . . . . . . . . . . . . 35 + 5.6.2. Non-HTTP APIs . . . . . . . . . . . . . . . . . . . . 35 + 5.6.3. Retrieval Algorithm . . . . . . . . . . . . . . . . . 36 + 6. Implementation Considerations . . . . . . . . . . . . . . . . 38 + 6.1. Limits . . . . . . . . . . . . . . . . . . . . . . . . . 38 + 6.2. Application Programming Interfaces . . . . . . . . . . . 38 + 6.3. IDNA Dependency and Migration . . . . . . . . . . . . . . 38 + 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 39 + 7.1. Third-Party Cookies . . . . . . . . . . . . . . . . . . . 39 + 7.2. Cookie policy . . . . . . . . . . . . . . . . . . . . . . 40 + 7.3. User Controls . . . . . . . . . . . . . . . . . . . . . . 40 + 7.4. Expiration Dates . . . . . . . . . . . . . . . . . . . . 40 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 41 + 8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 41 + 8.2. Ambient Authority . . . . . . . . . . . . . . . . . . . . 41 + 8.3. Clear Text . . . . . . . . . . . . . . . . . . . . . . . 42 + 8.4. Session Identifiers . . . . . . . . . . . . . . . . . . . 42 + 8.5. Weak Confidentiality . . . . . . . . . . . . . . . . . . 43 + 8.6. Weak Integrity . . . . . . . . . . . . . . . . . . . . . 44 + 8.7. Reliance on DNS . . . . . . . . . . . . . . . . . . . . . 44 + 8.8. SameSite Cookies . . . . . . . . . . . . . . . . . . . . 45 + 8.8.1. Defense in depth . . . . . . . . . . . . . . . . . . 45 + 8.8.2. Top-level Navigations . . . . . . . . . . . . . . . . 45 + 8.8.3. Mashups and Widgets . . . . . . . . . . . . . . . . . 46 + 8.8.4. Server-controlled . . . . . . . . . . . . . . . . . . 46 + 8.8.5. Reload navigations . . . . . . . . . . . . . . . . . 46 + 8.8.6. Top-level requests with "unsafe" methods . . . . . . 47 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47 + 9.1. Cookie . . . . . . . . . . . . . . . . . . . . . . . . . 48 + 9.2. Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . 48 + 9.3. Cookie Attribute Registry . . . . . . . . . . . . . . . . 48 + 9.3.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 48 + 9.3.2. Registration . . . . . . . . . . . . . . . . . . . . 49 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 49 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 49 + 10.2. Informative References . . . . . . . . . . . . . . . . . 51 + Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . 53 + A.1. draft-ietf-httpbis-rfc6265bis-00 . . . . . . . . . . . . 53 + A.2. draft-ietf-httpbis-rfc6265bis-01 . . . . . . . . . . . . 53 + A.3. draft-ietf-httpbis-rfc6265bis-02 . . . . . . . . . . . . 54 + A.4. draft-ietf-httpbis-rfc6265bis-03 . . . . . . . . . . . . 54 + A.5. draft-ietf-httpbis-rfc6265bis-04 . . . . . . . . . . . . 55 + A.6. draft-ietf-httpbis-rfc6265bis-05 . . . . . . . . . . . . 55 + A.7. draft-ietf-httpbis-rfc6265bis-06 . . . . . . . . . . . . 55 + A.8. draft-ietf-httpbis-rfc6265bis-07 . . . . . . . . . . . . 56 + A.9. draft-ietf-httpbis-rfc6265bis-08 . . . . . . . . . . . . 56 + Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 57 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57 1. Introduction This document defines the HTTP Cookie and Set-Cookie header fields. Using the Set-Cookie header field, an HTTP server can pass name/value pairs and associated metadata (called cookies) to a user agent. When the user agent makes subsequent requests to the server, the user agent uses the metadata and other information to determine whether to - return the name/value pairs in the Cookie header. + return the name/value pairs in the Cookie header field. Although simple on their surface, cookies have a number of complexities. For example, the server indicates a scope for each cookie when sending it to the user agent. The scope indicates the maximum amount of time in which the user agent should return the cookie, the servers to which the user agent should return the cookie, and the URI schemes for which the cookie is applicable. For historical reasons, cookies contain a number of security and privacy infelicities. For example, a server can indicate that a @@ -181,30 +194,30 @@ To maximize interoperability with user agents, servers SHOULD limit themselves to the well-behaved profile defined in Section 4 when generating cookies. User agents MUST implement the more liberal processing rules defined in Section 5, in order to maximize interoperability with existing servers that do not conform to the well-behaved profile defined in Section 4. - This document specifies the syntax and semantics of these headers as - they are actually used on the Internet. In particular, this document - does not create new syntax or semantics beyond those in use today. - The recommendations for cookie generation provided in Section 4 - represent a preferred subset of current server behavior, and even the - more liberal cookie processing algorithm provided in Section 5 does - not recommend all of the syntactic and semantic variations in use - today. Where some existing software differs from the recommended - protocol in significant ways, the document contains a note explaining - the difference. + This document specifies the syntax and semantics of these header + fields as they are actually used on the Internet. In particular, + this document does not create new syntax or semantics beyond those in + use today. The recommendations for cookie generation provided in + Section 4 represent a preferred subset of current server behavior, + and even the more liberal cookie processing algorithm provided in + Section 5 does not recommend all of the syntactic and semantic + variations in use today. Where some existing software differs from + the recommended protocol in significant ways, the document contains a + note explaining the difference. This document obsoletes [RFC6265]. 2. Conventions 2.1. Conformance Criteria The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. @@ -227,115 +240,123 @@ The following core rules are included by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTLs (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), NUL (null octet), OCTET (any 8-bit sequence of data except NUL), SP (space), HTAB (horizontal tab), CHAR (any [USASCII] character), VCHAR (any visible [USASCII] character), and WSP (whitespace). The OWS (optional whitespace) and BWS (bad whitespace) rules are - defined in Section 3.2.3 of [RFC7230]. + defined in Section 5.6.3 of [HTTPSEM]. 2.3. Terminology The terms "user agent", "client", "server", "proxy", and "origin server" have the same meaning as in the HTTP/1.1 specification - ([RFC7230], Section 2). + ([HTTPSEM], Section 3). The request-host is the name of the host, as known by the user agent, to which the user agent is sending an HTTP request or from which it is receiving an HTTP response (i.e., the name of the host to which it sent the corresponding HTTP request). - The term request-uri refers to "request-target" as defined in - Section 5.3 of [RFC7230]. + The term request-uri refers to "target URI" as defined in Section 7.1 + of [HTTPSEM]. Two sequences of octets are said to case-insensitively match each other if and only if they are equivalent under the i;ascii-casemap collation defined in [RFC4790]. The term string means a sequence of non-NUL octets. The terms "active document", "ancestor browsing context", "browsing - context", "dedicated worker", "Document", "WorkerGlobalScope", - "sandboxed origin browsing context flag", "parent browsing context", - "shared worker", "the worker's Documents", "nested browsing context", - and "top-level browsing context" are defined in [HTML]. + context", "dedicated worker", "Document", "nested browsing context", + "opaque origin", "parent browsing context", "sandboxed origin + browsing context flag", "shared worker", "the worker's Documents", + "top-level browsing context", and "WorkerGlobalScope" are defined in + [HTML]. "Service Workers" are defined in the Service Workers specification [SERVICE-WORKERS]. The term "origin", the mechanism of deriving an origin from a URI, and the "the same" matching algorithm for origins are defined in [RFC6454]. "Safe" HTTP methods include "GET", "HEAD", "OPTIONS", and "TRACE", as - defined in Section 4.2.1 of [RFC7231]. + defined in Section 9.2.1 of [HTTPSEM]. A domain's "public suffix" is the portion of a domain that is controlled by a public registry, such as "com", "co.uk", and "pvt.k12.wy.us". A domain's "registrable domain" is the domain's public suffix plus the label to its left. That is, for "https://www.site.example", the public suffix is "example", and the registrable domain is "site.example". Whenever possible, user agents SHOULD use an up-to-date public suffix list, such as the one maintained by the Mozilla project at [PSL]. The term "request", as well as a request's "client", "current url", - "method", and "target browsing context", are defined in [FETCH]. + "method", "target browsing context", and "url list", are defined in + [FETCH]. + + The term "non-HTTP APIs" refers to non-HTTP mechanisms used to set + and retrieve cookies, such as a web browser API that exposes cookies + to scripts. 3. Overview This section outlines a way for an origin server to send state information to a user agent and for the user agent to return the state information to the origin server. - To store state, the origin server includes a Set-Cookie header in an - HTTP response. In subsequent requests, the user agent returns a - Cookie request header to the origin server. The Cookie header - contains cookies the user agent received in previous Set-Cookie - headers. The origin server is free to ignore the Cookie header or - use its contents for an application-defined purpose. + To store state, the origin server includes a Set-Cookie header field + in an HTTP response. In subsequent requests, the user agent returns + a Cookie request header field to the origin server. The Cookie + header field contains cookies the user agent received in previous + Set-Cookie header fields. The origin server is free to ignore the + Cookie header field or use its contents for an application-defined + purpose. - Origin servers MAY send a Set-Cookie response header with any - response. User agents MAY ignore Set-Cookie headers contained in - responses with 100-level status codes but MUST process Set-Cookie - headers contained in other responses (including responses with 400- - and 500-level status codes). An origin server can include multiple - Set-Cookie header fields in a single response. The presence of a - Cookie or a Set-Cookie header field does not preclude HTTP caches - from storing and reusing a response. + Origin servers MAY send a Set-Cookie response header field with any + response. An origin server can include multiple Set-Cookie header + fields in a single response. The presence of a Cookie or a Set- + Cookie header field does not preclude HTTP caches from storing and + reusing a response. Origin servers SHOULD NOT fold multiple Set-Cookie header fields into a single header field. The usual mechanism for folding HTTP headers - fields (i.e., as defined in Section 3.2.2 of [RFC7230]) might change + fields (i.e., as defined in Section 5.3 of [HTTPSEM]) might change the semantics of the Set-Cookie header field because the %x2C (",") character is used by Set-Cookie in a way that conflicts with such folding. + User agents MAY ignore Set-Cookie header fieldss based on response + status codes or the user agent's cookie policy (see Section 5.3). + 3.1. Examples - Using the Set-Cookie header, a server can send the user agent a short - string in an HTTP response that the user agent will return in future - HTTP requests that are within the scope of the cookie. For example, - the server can send the user agent a "session identifier" named SID - with the value 31d4d96e407aad42. The user agent then returns the - session identifier in subsequent requests. + Using the Set-Cookie header field, a server can send the user agent a + short string in an HTTP response that the user agent will return in + future HTTP requests that are within the scope of the cookie. For + example, the server can send the user agent a "session identifier" + named SID with the value 31d4d96e407aad42. The user agent then + returns the session identifier in subsequent requests. == Server -> User Agent == Set-Cookie: SID=31d4d96e407aad42 == User Agent -> Server == Cookie: SID=31d4d96e407aad42 + The server can alter the default scope of the cookie using the Path and Domain attributes. For example, the server can instruct the user agent to return the cookie to every path and every subdomain of site.example. == Server -> User Agent == Set-Cookie: SID=31d4d96e407aad42; Path=/; Domain=site.example == User Agent -> Server == @@ -350,23 +371,22 @@ the more sensitive session identifier (see Section 4.1.2). == Server -> User Agent == Set-Cookie: SID=31d4d96e407aad42; Path=/; Secure; HttpOnly Set-Cookie: lang=en-US; Path=/; Domain=site.example == User Agent -> Server == Cookie: SID=31d4d96e407aad42; lang=en-US - - Notice that the Cookie header above contains two cookies, one named - SID and one named lang. If the server wishes the user agent to + Notice that the Cookie header field above contains two cookies, one + named SID and one named lang. If the server wishes the user agent to persist the cookie over multiple "sessions" (e.g., user agent restarts), the server can specify an expiration date in the Expires attribute. Note that the user agent might delete the cookie before the expiration date if the user agent's cookie store exceeds its quota or if the user manually deletes the server's cookie. == Server -> User Agent == Set-Cookie: lang=en-US; Expires=Wed, 09 Jun 2021 10:18:14 GMT @@ -366,69 +386,69 @@ the expiration date if the user agent's cookie store exceeds its quota or if the user manually deletes the server's cookie. == Server -> User Agent == Set-Cookie: lang=en-US; Expires=Wed, 09 Jun 2021 10:18:14 GMT == User Agent -> Server == Cookie: SID=31d4d96e407aad42; lang=en-US + Finally, to remove a cookie, the server returns a Set-Cookie header - with an expiration date in the past. The server will be successful - in removing the cookie only if the Path and the Domain attribute in - the Set-Cookie header match the values used when the cookie was - created. + field with an expiration date in the past. The server will be + successful in removing the cookie only if the Path and the Domain + attribute in the Set-Cookie header field match the values used when + the cookie was created. == Server -> User Agent == Set-Cookie: lang=; Expires=Sun, 06 Nov 1994 08:49:37 GMT == User Agent -> Server == Cookie: SID=31d4d96e407aad42 4. Server Requirements This section describes the syntax and semantics of a well-behaved - profile of the Cookie and Set-Cookie headers. + profile of the Cookie and Set-Cookie header fields. 4.1. Set-Cookie - The Set-Cookie HTTP response header is used to send cookies from the - server to the user agent. + The Set-Cookie HTTP response header field is used to send cookies + from the server to the user agent. 4.1.1. Syntax - Informally, the Set-Cookie response header contains the header name - "Set-Cookie" followed by a ":" and a cookie. Each cookie begins with - a name-value-pair, followed by zero or more attribute-value pairs. - Servers SHOULD NOT send Set-Cookie headers that fail to conform to - the following grammar: + Informally, the Set-Cookie response header field contains a cookie, + which begins with a name-value-pair, followed by zero or more + attribute-value pairs. Servers SHOULD NOT send Set-Cookie header + fields that fail to conform to the following grammar: - set-cookie-header = "Set-Cookie:" SP BWS set-cookie-string + set-cookie = set-cookie-string set-cookie-string = BWS cookie-pair *( BWS ";" OWS cookie-av ) cookie-pair = cookie-name BWS "=" BWS cookie-value cookie-name = 1*cookie-octet cookie-value = *cookie-octet / ( DQUOTE *cookie-octet DQUOTE ) cookie-octet = %x21 / %x23-2B / %x2D-3A / %x3C-5B / %x5D-7E / %x80-FF ; octets excluding CTLs, ; whitespace DQUOTE, comma, semicolon, ; and backslash cookie-av = expires-av / max-age-av / domain-av / path-av / secure-av / httponly-av / samesite-av / extension-av expires-av = "Expires" BWS "=" BWS sane-cookie-date sane-cookie-date = - + max-age-av = "Max-Age" BWS "=" BWS non-zero-digit *DIGIT ; In practice, both expires-av and max-age-av ; are limited to dates representable by the ; user agent. non-zero-digit = %x31-39 ; digits 1 through 9 domain-av = "Domain" BWS "=" BWS domain-value domain-value = ; defined in [RFC1034], Section 3.5, as ; enhanced by [RFC1123], Section 2.1 @@ -448,57 +468,57 @@ The semantics of the cookie-value are not defined by this document. To maximize compatibility with user agents, servers that wish to store arbitrary data in a cookie-value SHOULD encode that data, for example, using Base64 [RFC4648]. Per the grammar above, the cookie-value MAY be wrapped in DQUOTE characters. Note that in this case, the initial and trailing DQUOTE characters are not stripped. They are part of the cookie-value, and - will be included in Cookie headers sent to the server. + will be included in Cookie header fields sent to the server. The portions of the set-cookie-string produced by the cookie-av term are known as attributes. To maximize compatibility with user agents, servers SHOULD NOT produce two attributes with the same name in the - same set-cookie-string. (See Section 5.4 for how user agents handle + same set-cookie-string. (See Section 5.5 for how user agents handle this case.) Servers SHOULD NOT include more than one Set-Cookie header field in - the same response with the same cookie-name. (See Section 5.3 for + the same response with the same cookie-name. (See Section 5.4 for how user agents handle this case.) - If a server sends multiple responses containing Set-Cookie headers - concurrently to the user agent (e.g., when communicating with the - user agent over multiple sockets), these responses create a "race + If a server sends multiple responses containing Set-Cookie header + fields concurrently to the user agent (e.g., when communicating with + the user agent over multiple sockets), these responses create a "race condition" that can lead to unpredictable behavior. NOTE: Some existing user agents differ in their interpretation of two-digit years. To avoid compatibility issues, servers SHOULD use the rfc1123-date format, which requires a four-digit year. NOTE: Some user agents store and process dates in cookies as 32-bit UNIX time_t values. Implementation bugs in the libraries supporting time_t processing on some systems might cause such user agents to process dates after the year 2038 incorrectly. 4.1.2. Semantics (Non-Normative) - This section describes simplified semantics of the Set-Cookie header. - These semantics are detailed enough to be useful for understanding - the most common uses of cookies by servers. The full semantics are - described in Section 5. + This section describes simplified semantics of the Set-Cookie header + field. These semantics are detailed enough to be useful for + understanding the most common uses of cookies by servers. The full + semantics are described in Section 5. - When the user agent receives a Set-Cookie header, the user agent - stores the cookie together with its attributes. Subsequently, when - the user agent makes an HTTP request, the user agent includes the - applicable, non-expired cookies in the Cookie header. + When the user agent receives a Set-Cookie header field, the user + agent stores the cookie together with its attributes. Subsequently, + when the user agent makes an HTTP request, the user agent includes + the applicable, non-expired cookies in the Cookie header field. If the user agent receives a new cookie with the same cookie-name, domain-value, and path-value as a cookie that it has already stored, the existing cookie is evicted and replaced with the new cookie. Notice that servers can delete cookies by sending the user agent a new cookie with an Expires attribute with a value in the past. Unless the cookie's attributes indicate otherwise, the cookie is returned only to the origin server (and not, for example, to any subdomains), and it expires at the end of the current session (as @@ -529,44 +549,45 @@ Age attribute has precedence and controls the expiration date of the cookie. If a cookie has neither the Max-Age nor the Expires attribute, the user agent will retain the cookie until "the current session is over" (as defined by the user agent). 4.1.2.3. The Domain Attribute The Domain attribute specifies those hosts to which the cookie will be sent. For example, if the value of the Domain attribute is "site.example", the user agent will include the cookie in the Cookie - header when making HTTP requests to site.example, www.site.example, - and www.corp.site.example. (Note that a leading %x2E ("."), if - present, is ignored even though that character is not permitted, but - a trailing %x2E ("."), if present, will cause the user agent to - ignore the attribute.) If the server omits the Domain attribute, the - user agent will return the cookie only to the origin server. + header field when making HTTP requests to site.example, + www.site.example, and www.corp.site.example. (Note that a leading + %x2E ("."), if present, is ignored even though that character is not + permitted, but a trailing %x2E ("."), if present, will cause the user + agent to ignore the attribute.) If the server omits the Domain + attribute, the user agent will return the cookie only to the origin + server. WARNING: Some existing user agents treat an absent Domain attribute as if the Domain attribute were present and contained the current host name. For example, if site.example returns a Set-Cookie header - without a Domain attribute, these user agents will erroneously send - the cookie to www.site.example as well. + field without a Domain attribute, these user agents will erroneously + send the cookie to www.site.example as well. The user agent will reject cookies unless the Domain attribute specifies a scope for the cookie that would include the origin server. For example, the user agent will accept a cookie with a Domain attribute of "site.example" or of "foo.site.example" from foo.site.example, but the user agent will not accept a cookie with a Domain attribute of "bar.site.example" or of "baz.foo.site.example". NOTE: For security reasons, many user agents are configured to reject Domain attributes that correspond to "public suffixes". For example, some user agents will reject Domain attributes of "com" or "co.uk". - (See Section 5.4 for more information.) + (See Section 5.5 for more information.) 4.1.2.4. The Path Attribute The scope of each cookie is limited to a set of paths, controlled by the Path attribute. If the server omits the Path attribute, the user agent will use the "directory" of the request-uri's path component as the default value. (See Section 5.1.4 for more details.) The user agent will include the cookie in an HTTP request only if the path portion of the request-uri matches (or is a subdirectory of) the @@ -589,41 +610,40 @@ Although seemingly useful for protecting cookies from active network attackers, the Secure attribute protects only the cookie's confidentiality. An active network attacker can overwrite Secure cookies from an insecure channel, disrupting their integrity (see Section 8.6 for more details). 4.1.2.6. The HttpOnly Attribute The HttpOnly attribute limits the scope of the cookie to HTTP requests. In particular, the attribute instructs the user agent to - omit the cookie when providing access to cookies via "non-HTTP" APIs - (such as a web browser API that exposes cookies to scripts). + omit the cookie when providing access to cookies via non-HTTP APIs. Note that the HttpOnly attribute is independent of the Secure attribute: a cookie can have both the HttpOnly and the Secure attribute. 4.1.2.7. The SameSite Attribute The "SameSite" attribute limits the scope of the cookie such that it will only be attached to requests if those requests are same-site, as defined by the algorithm in Section 5.2. For example, requests for "https://site.example/sekrit-image" will attach same-site cookies if and only if initiated from a context whose "site for cookies" is an origin with a scheme and registered domain of "https" and "site.example" respectively. If the "SameSite" attribute's value is "Strict", the cookie will only be sent along with "same-site" requests. If the value is "Lax", the cookie will be sent with same-site requests, and with "cross-site" - top-level navigations, as described in Section 5.3.7.1. If the value + top-level navigations, as described in Section 5.4.7.1. If the value is "None", the cookie will be sent with same-site and cross-site requests. If the "SameSite" attribute's value is something other than these three known keywords, the attribute's value will be subject to a default enforcement mode that is equivalent to "Lax". The "SameSite" attribute affects cookie creation as well as delivery. Cookies which assert "SameSite=Lax" or "SameSite=Strict" cannot be set in responses to cross-site subresource requests, or cross-site nested navigations. They can be set along with any top-level navigation, cross-site or otherwise. @@ -632,34 +652,35 @@ Section 8.5 and Section 8.6 of this document spell out some of the drawbacks of cookies' historical implementation. In particular, it is impossible for a server to have confidence that a given cookie was set with a particular set of attributes. In order to provide such confidence in a backwards-compatible way, two common sets of requirements can be inferred from the first few characters of the cookie's name. The normative requirements for the prefixes described below are - detailed in the storage model algorithm defined in Section 5.4. + detailed in the storage model algorithm defined in Section 5.5. 4.1.3.1. The "__Secure-" Prefix If a cookie's name begins with a case-sensitive match for the string "__Secure-", then the cookie will have been set with a "Secure" attribute. - For example, the following "Set-Cookie" header would be rejected by a - conformant user agent, as it does not have a "Secure" attribute. + For example, the following "Set-Cookie" header field would be + rejected by a conformant user agent, as it does not have a "Secure" + attribute. Set-Cookie: __Secure-SID=12345; Domain=site.example - Whereas the following "Set-Cookie" header would be accepted: + Whereas the following "Set-Cookie" header field would be accepted: Set-Cookie: __Secure-SID=12345; Domain=site.example; Secure 4.1.3.2. The "__Host-" Prefix If a cookie's name begins with a case-sensitive match for the string "__Host-", then the cookie will have been set with a "Secure" attribute, a "Path" attribute with a value of "/", and no "Domain" attribute. @@ -686,67 +707,68 @@ While the following would be accepted if set from a secure origin (e.g. "https://site.example/"), and rejected otherwise: Set-Cookie: __Host-SID=12345; Secure; Path=/ 4.2. Cookie 4.2.1. Syntax The user agent sends stored cookies to the origin server in the - Cookie header. If the server conforms to the requirements in + Cookie header field. If the server conforms to the requirements in Section 4.1 (and the user agent conforms to the requirements in - Section 5), the user agent will send a Cookie header that conforms to - the following grammar: + Section 5), the user agent will send a Cookie header field that + conforms to the following grammar: - cookie-header = "Cookie:" SP cookie-string + cookie = cookie-string cookie-string = cookie-pair *( ";" SP cookie-pair ) 4.2.2. Semantics Each cookie-pair represents a cookie stored by the user agent. The cookie-pair contains the cookie-name and cookie-value the user agent - received in the Set-Cookie header. + received in the Set-Cookie header field. Notice that the cookie attributes are not returned. In particular, - the server cannot determine from the Cookie header alone when a - cookie will expire, for which hosts the cookie is valid, for which - paths the cookie is valid, or whether the cookie was set with the - Secure or HttpOnly attributes. + the server cannot determine from the Cookie field alone when a cookie + will expire, for which hosts the cookie is valid, for which paths the + cookie is valid, or whether the cookie was set with the Secure or + HttpOnly attributes. - The semantics of individual cookies in the Cookie header are not - defined by this document. Servers are expected to imbue these + The semantics of individual cookies in the Cookie header field are + not defined by this document. Servers are expected to imbue these cookies with application-specific semantics. - Although cookies are serialized linearly in the Cookie header, + Although cookies are serialized linearly in the Cookie header field, servers SHOULD NOT rely upon the serialization order. In particular, - if the Cookie header contains two cookies with the same name (e.g., - that were set with different Path or Domain attributes), servers - SHOULD NOT rely upon the order in which these cookies appear in the - header. + if the Cookie header field contains two cookies with the same name + (e.g., that were set with different Path or Domain attributes), + servers SHOULD NOT rely upon the order in which these cookies appear + in the header field. 5. User Agent Requirements - This section specifies the Cookie and Set-Cookie headers in + This section specifies the Cookie and Set-Cookie header fields in sufficient detail that a user agent implementing these requirements precisely can interoperate with existing servers (even those that do not conform to the well-behaved profile described in Section 4). A user agent could enforce more restrictions than those specified - herein (e.g., for the sake of improved security); however, - experiments have shown that such strictness reduces the likelihood - that a user agent will be able to interoperate with existing servers. + herein (e.g., restrictions specified by its cookie policy, described + in Section 7.2). However, such additional restrictions may reduce + the likelihood that a user agent will be able to interoperate with + existing servers. 5.1. Subcomponent Algorithms This section defines some algorithms used by user agents to process - specific subcomponents of the Cookie and Set-Cookie headers. + specific subcomponents of the Cookie and Set-Cookie header fields. 5.1.1. Dates The user agent MUST use an algorithm equivalent to the following algorithm to parse a cookie-date. Note that the various boolean flags defined as a part of the algorithm (i.e., found-time, found- day-of-month, found-month, found-year) are initially "not set". 1. Using the grammar below, divide the cookie-date into date-tokens. @@ -860,25 +882,21 @@ domain string is a %x2E (".") character. - The string is a host name (i.e., not an IP address). 5.1.4. Paths and Path-Match The user agent MUST use an algorithm equivalent to the following algorithm to compute the default-path of a cookie: 1. Let uri-path be the path portion of the request-uri if such a - portion exists (and empty otherwise). For example, if the - request-uri contains just a path (and optional query string), - then the uri-path is that path (without the %x3F ("?") character - or query string), and if the request-uri contains a full - absoluteURI, the uri-path is the path component of that URI. + portion exists (and empty otherwise). 2. If the uri-path is empty or if the first character of the uri- path is not a %x2F ("/") character, output %x2F ("/") and skip the remaining steps. 3. If the uri-path contains no more than one %x2F ("/") character, output %x2F ("/") and skip the remaining step. 4. Output the characters of the uri-path from the first character up to, but not including, the right-most %x2F ("/"). @@ -894,46 +912,41 @@ * The cookie-path is a prefix of the request-path, and the last character of the cookie-path is %x2F ("/"). * The cookie-path is a prefix of the request-path, and the first character of the request-path that is not included in the cookie- path is a %x2F ("/") character. 5.2. "Same-site" and "cross-site" Requests - Two origins, A and B, are considered same-site if the following - algorithm returns true: - - 1. If A and B are both the same globally unique identifier, return - true. - - 2. If A and B are both scheme/host/port triples: - - 1. If A's scheme does not equal B's scheme, return false. - - 2. Let hostA be A's host, and hostB be B's host. - - 3. If hostA equals hostB and hostA's registrable domain is null, - return true. + Two origins are same-site if they satisfy the "same site" criteria + defined in [SAMESITE]. A request is "same-site" if the following + criteria are true: - 4. If hostA's registrable domain equals hostB's registrable - domain and is non-null, return true. + 1. The request is not the result of a cross-site redirect. That is, + the origin of every url in the request's url list is same-site + with the request's current url's origin. - 3. Return false. + 2. The request is not the result of a reload navigation triggered + through a user interface element (as defined by the user agent; + e.g., a request triggered by the user clicking a refresh button + on a toolbar). - Note: The port component of the origins is not considered. + 3. The request's current url's origin is same-site with the + request's client's "site for cookies" (which is an origin), or if + the request has no client or the request's client is null. - A request is "same-site" if its target's URI's origin is same-site - with the request's client's "site for cookies" (which is an origin), - or if the request has no client. The request is otherwise "cross- - site". + Requests which are the result of a reload navigation triggered + through a user interface element are same-site if the reloaded + document was originally navigated to via a same-site request. A + request that is not "same-site" is instead "cross-site". The request's client's "site for cookies" is calculated depending upon its client's type, as described in the following subsections: 5.2.1. Document-based requests The URI displayed in a user agent's address bar is the only security context directly exposed to users, and therefore the only signal users can reasonably rely upon to determine whether or not they trust a particular website. The origin of that URI represents the context @@ -944,21 +957,21 @@ For a document displayed in a top-level browsing context, we can stop here: the document's "site for cookies" is the top-level origin. For documents which are displayed in nested browsing contexts, we need to audit the origins of each of a document's ancestor browsing contexts' active documents in order to account for the "multiple- nested scenarios" described in Section 4 of [RFC7034]. A document's "site for cookies" is the top-level origin if and only if the top- level origin is same-site with the document's origin, and with each of the document's ancestor documents' origins. Otherwise its "site - for cookies" is an origin set to a globally unique identifier. + for cookies" is an origin set to an opaque origin. Given a Document ("document"), the following algorithm returns its "site for cookies": 1. Let "top-document" be the active document in "document"'s browsing context's top-level browsing context. 2. Let "top-origin" be the origin of "top-document"'s URI if "top- document"'s sandboxed origin browsing context flag is set, and "top-document"'s origin otherwise. @@ -966,21 +979,21 @@ 3. Let "documents" be a list containing "document" and each of "document"'s ancestor browsing contexts' active documents. 4. For each "item" in "documents": 1. Let "origin" be the origin of "item"'s URI if "item"'s sandboxed origin browsing context flag is set, and "item"'s origin otherwise. 2. If "origin" is not same-site with "top-origin", return an - origin set to a globally unique identifier. + origin set to an opaque origin. 5. Return "top-origin". 5.2.2. Worker-based requests Worker-driven requests aren't as clear-cut as document-driven requests, as there isn't a clear link between a top-level browsing context and a worker. This is especially true for Service Workers [SERVICE-WORKERS], which may execute code in the background, without any document visible at all. @@ -993,36 +1006,36 @@ 5.2.2.1. Dedicated and Shared Workers Dedicated workers are simple, as each dedicated worker is bound to one and only one document. Requests generated from a dedicated worker (via "importScripts", "XMLHttpRequest", "fetch()", etc) define their "site for cookies" as that document's "site for cookies". Shared workers may be bound to multiple documents at once. As it is quite possible for those documents to have distinct "site for cookies" values, the worker's "site for cookies" will be an origin - set to a globally unique identifier in cases where the values are not - all same-site with the worker's origin, and the worker's origin in - cases where the values agree. + set to an opaque origin in cases where the values are not all same- + site with the worker's origin, and the worker's origin in cases where + the values agree. Given a WorkerGlobalScope ("worker"), the following algorithm returns its "site for cookies": 1. Let "site" be "worker"'s origin. 2. For each "document" in "worker"'s Documents: 1. Let "document-site" be "document"'s "site for cookies" (as defined in Section 5.2.1). 2. If "document-site" is not same-site with "site", return an - origin set to a globally unique identifier. + origin set to an opaque origin. 3. Return "site". 5.2.2.2. Service Workers Service Workers are more complicated, as they act as a completely separate execution context with only tangential relationship to the Document which registered them. Requests which simply pass through a Service Worker will be handled @@ -1033,69 +1046,93 @@ Requests which are initiated by the Service Worker itself (via a direct call to "fetch()", for instance), on the other hand, will have a client which is a ServiceWorkerGlobalScope. Its "site for cookies" will be the Service Worker's URI's origin. Given a ServiceWorkerGlobalScope ("worker"), the following algorithm returns its "site for cookies": 1. Return "worker"'s origin. -5.3. The Set-Cookie Header +5.3. Ignoring Set-Cookie Header Fields + + User agents MAY ignore Set-Cookie header fields contained in + responses with 100-level status codes or based on its cookie policy + (see Section 7.2). + + All other Set-Cookie header fields SHOULD be processed according to + Section 5.4. That is, Set-Cookie header fields contained in + responses with non-100-level status codes (including those in + responses with 400- and 500-level status codes) SHOULD be processed + unless ignored according to the user agent's cookie policy. + +5.4. The Set-Cookie Header Field When a user agent receives a Set-Cookie header field in an HTTP response, the user agent MAY ignore the Set-Cookie header field in - its entirety. For example, the user agent might wish to block - responses to "third-party" requests from setting cookies (see - Section 7.1). + its entirety (see Section 5.3). If the user agent does not ignore the Set-Cookie header field in its entirety, the user agent MUST parse the field-value of the Set-Cookie header field as a set-cookie-string (defined below). NOTE: The algorithm below is more permissive than the grammar in Section 4.1. For example, the algorithm strips leading and trailing whitespace from the cookie name and value (but maintains internal whitespace), whereas the grammar in Section 4.1 forbids whitespace in - these positions. User agents use this algorithm so as to - interoperate with servers that do not follow the recommendations in - Section 4. + these positions. In addition, the algorithm below accommodates some + characters that are not cookie-octets according to the grammar in + Section 4.1. User agents use this algorithm so as to interoperate + with servers that do not follow the recommendations in Section 4. + + NOTE: As set-cookie-string may originate from a non-HTTP API, it is + not guaranteed to be free of CTL characters, so this algorithm + handles them explicitly. A user agent MUST use an algorithm equivalent to the following algorithm to parse a set-cookie-string: - 1. If the set-cookie-string contains a %x3B (";") character: + 1. If the set-cookie-string contains a %x0D (CR), %x0A (LF), or %x00 + (NUL) octet, then set the set-cookie-string equal to all the + characters of set-cookie-string up to, but not including, the + first such octet. + + 2. If the set-cookie-string contains a %x00-1F / %x7F (CTL) + character: Abort these steps and ignore the set-cookie-string + entirely. + + 3. If the set-cookie-string contains a %x3B (";") character: 1. The name-value-pair string consists of the characters up to, but not including, the first %x3B (";"), and the unparsed- attributes consist of the remainder of the set-cookie-string (including the %x3B (";") in question). Otherwise: 1. The name-value-pair string consists of all the characters contained in the set-cookie-string, and the unparsed- attributes is the empty string. - 2. If the name-value-pair string lacks a %x3D ("=") character, then + 4. If the name-value-pair string lacks a %x3D ("=") character, then the name string is empty, and the value string is the value of name-value-pair. Otherwise, the name string consists of the characters up to, but not including, the first %x3D ("=") character, and the (possibly empty) value string consists of the characters after the first %x3D ("=") character. - 3. Remove any leading or trailing WSP characters from the name + 5. Remove any leading or trailing WSP characters from the name string and the value string. - 4. The cookie-name is the name string, and the cookie-value is the + 6. The cookie-name is the name string, and the cookie-value is the value string. The user agent MUST use an algorithm equivalent to the following algorithm to parse the unparsed-attributes: 1. If the unparsed-attributes string is empty, skip the rest of these steps. 2. Discard the first character of the unparsed-attributes (which will be a %x3B (";") character). @@ -1130,24 +1167,24 @@ 6. Process the attribute-name and attribute-value according to the requirements in the following subsections. (Notice that attributes with unrecognized attribute-names are ignored.) 7. Return to Step 1 of this algorithm. When the user agent finishes parsing the set-cookie-string, the user agent is said to "receive a cookie" from the request-uri with name cookie-name, value cookie-value, and attributes cookie-attribute- - list. (See Section 5.4 for additional requirements triggered by + list. (See Section 5.5 for additional requirements triggered by receiving a cookie.) -5.3.1. The Expires Attribute +5.4.1. The Expires Attribute If the attribute-name case-insensitively matches the string "Expires", the user agent MUST process the cookie-av as follows. 1. Let the expiry-time be the result of parsing the attribute-value as cookie-date (see Section 5.1.1). 2. If the attribute-value failed to parse as a cookie date, ignore the cookie-av. @@ -1155,42 +1192,42 @@ represent, the user agent MAY replace the expiry-time with the last representable date. 4. If the expiry-time is earlier than the earliest date the user agent can represent, the user agent MAY replace the expiry-time with the earliest representable date. 5. Append an attribute to the cookie-attribute-list with an attribute-name of Expires and an attribute-value of expiry-time. -5.3.2. The Max-Age Attribute +5.4.2. The Max-Age Attribute If the attribute-name case-insensitively matches the string "Max- Age", the user agent MUST process the cookie-av as follows. 1. If the first character of the attribute-value is not a DIGIT or a "-" character, ignore the cookie-av. 2. If the remainder of attribute-value contains a non-DIGIT character, ignore the cookie-av. 3. Let delta-seconds be the attribute-value converted to an integer. 4. If delta-seconds is less than or equal to zero (0), let expiry- time be the earliest representable date and time. Otherwise, let the expiry-time be the current date and time plus delta-seconds seconds. 5. Append an attribute to the cookie-attribute-list with an attribute-name of Max-Age and an attribute-value of expiry-time. -5.3.3. The Domain Attribute +5.4.3. The Domain Attribute If the attribute-name case-insensitively matches the string "Domain", the user agent MUST process the cookie-av as follows. 1. If the attribute-value is empty, the behavior is undefined. However, the user agent SHOULD ignore the cookie-av entirely. 2. If the first character of the attribute-value string is %x2E ("."): @@ -1199,131 +1236,171 @@ Otherwise: 1. Let cookie-domain be the entire attribute-value. 3. Convert the cookie-domain to lower case. 4. Append an attribute to the cookie-attribute-list with an attribute-name of Domain and an attribute-value of cookie-domain. -5.3.4. The Path Attribute +5.4.4. The Path Attribute If the attribute-name case-insensitively matches the string "Path", the user agent MUST process the cookie-av as follows. 1. If the attribute-value is empty or if the first character of the attribute-value is not %x2F ("/"): 1. Let cookie-path be the default-path. Otherwise: 1. Let cookie-path be the attribute-value. 2. Append an attribute to the cookie-attribute-list with an attribute-name of Path and an attribute-value of cookie-path. -5.3.5. The Secure Attribute +5.4.5. The Secure Attribute If the attribute-name case-insensitively matches the string "Secure", the user agent MUST append an attribute to the cookie-attribute-list with an attribute-name of Secure and an empty attribute-value. -5.3.6. The HttpOnly Attribute +5.4.6. The HttpOnly Attribute If the attribute-name case-insensitively matches the string "HttpOnly", the user agent MUST append an attribute to the cookie- attribute-list with an attribute-name of HttpOnly and an empty attribute-value. -5.3.7. The SameSite Attribute +5.4.7. The SameSite Attribute If the attribute-name case-insensitively matches the string "SameSite", the user agent MUST process the cookie-av as follows: 1. Let "enforcement" be "Default". 2. If cookie-av's attribute-value is a case-insensitive match for "None", set "enforcement" to "None". 3. If cookie-av's attribute-value is a case-insensitive match for "Strict", set "enforcement" to "Strict". 4. If cookie-av's attribute-value is a case-insensitive match for "Lax", set "enforcement" to "Lax". 5. Append an attribute to the cookie-attribute-list with an attribute-name of "SameSite" and an attribute-value of "enforcement". - Note: This algorithm maps the "None" value, as well as any unknown - value, to the "None" behavior, which is helpful for backwards - compatibility when introducing new variants. - -5.3.7.1. "Strict" and "Lax" enforcement +5.4.7.1. "Strict" and "Lax" enforcement Same-site cookies in "Strict" enforcement mode will not be sent along with top-level navigations which are triggered from a cross-site document context. As discussed in Section 8.8.2, this might or might not be compatible with existing session management systems. In the interests of providing a drop-in mechanism that mitigates the risk of CSRF attacks, developers may set the "SameSite" attribute in a "Lax" enforcement mode that carves out an exception which sends same-site cookies along with cross-site requests if and only if they are top- - level navigations which use a "safe" (in the [RFC7231] sense) HTTP + level navigations which use a "safe" (in the [HTTPSEM] sense) HTTP method. (Note that a request's method may be changed from POST to - GET for some redirects (see sections 6.4.2 and 6.4.3 of [RFC7231]); + GET for some redirects (see Sections 15.4.2 and 15.4.3 of [HTTPSEM]); in these cases, a request's "safe"ness is determined based on the method of the current redirect hop.) Lax enforcement provides reasonable defense in depth against CSRF attacks that rely on unsafe HTTP methods (like "POST"), but does not offer a robust defense against CSRF as a general category of attack: 1. Attackers can still pop up new windows or trigger top-level navigations in order to create a "same-site" request (as described in Section 5.2.1), which is only a speedbump along the road to exploitation. 2. Features like "" [prerendering] can be exploited to create "same-site" requests without the risk of user detection. When possible, developers should use a session management mechanism such as that described in Section 8.8.2 to mitigate the risk of CSRF more completely. -5.4. Storage Model +5.4.7.2. "Lax-Allowing-Unsafe" enforcement + + As discussed in Section 8.8.6, compatibility concerns may necessitate + the use of a "Lax-allowing-unsafe" enforcement mode that allows + cookies to be sent with a cross-site HTTP request if and only if it + is a top-level request, regardless of request method. That is, the + "Lax-allowing-unsafe" enforcement mode waives the requirement for the + HTTP request's method to be "safe" in the "SameSite" enforcement step + of the retrieval algorithm in Section 5.6.3. (All cookies, + regardless of "SameSite" enforcement mode, may be set for top-level + navigations, regardless of HTTP request method, as specified in + Section 5.5.) + + "Lax-allowing-unsafe" is not a distinct value of the "SameSite" + attribute. Rather, user agents MAY apply "Lax-allowing-unsafe" + enforcement only to cookies that did not explicitly specify a + "SameSite" attribute (i.e., those whose same-site-flag was set to + "Default" by default). To limit the scope of this compatibility + mode, user agents which apply "Lax-allowing-unsafe" enforcement + SHOULD restrict the enforcement to cookies which were created + recently. Deployment experience has shown a cookie age of 2 minutes + or less to be a reasonable limit. + + If the user agent uses "Lax-allowing-unsafe" enforcement, it MUST + apply the following modification to the retrieval algorithm defined + in Section 5.6.3: + + Replace the condition in the penultimate bullet point of step 1 of + the retrieval algorithm reading + + * The HTTP request associated with the retrieval uses a "safe" method. + + with + + * At least one of the following is true: + + 1. The HTTP request associated with the retrieval uses a "safe" method. + + 2. The cookie's same-site-flag is "Default" and the amount of time + elapsed since the cookie's creation-time is at most a duration of the + user agent's choosing. + +5.5. Storage Model The user agent stores the following fields about each cookie: name, value, expiry-time, domain, path, creation-time, last-access-time, persistent-flag, host-only-flag, secure-only-flag, http-only-flag, and same-site-flag. When the user agent "receives a cookie" from a request-uri with name cookie-name, value cookie-value, and attributes cookie-attribute- list, the user agent MUST process the cookie as follows: - 1. A user agent MAY ignore a received cookie in its entirety. For - example, the user agent might wish to block receiving cookies - from "third-party" responses or the user agent might not wish to - store cookies that exceed some size. + 1. A user agent MAY ignore a received cookie in its entirety. See + Section 5.3. 2. If cookie-name is empty and cookie-value is empty, abort these steps and ignore the cookie entirely. - 3. Create a new cookie with name cookie-name, value cookie-value. + 3. If the cookie-name or the cookie-value contains a %x00-1F / %x7F + (CTL) character, abort these steps and ignore the cookie + entirely. + + 4. Create a new cookie with name cookie-name, value cookie-value. Set the creation-time and the last-access-time to the current date and time. - 4. If the cookie-attribute-list contains an attribute with an + 5. If the cookie-attribute-list contains an attribute with an attribute-name of "Max-Age": 1. Set the cookie's persistent-flag to true. 2. Set the cookie's expiry-time to attribute-value of the last attribute in the cookie-attribute-list with an attribute- name of "Max-Age". Otherwise, if the cookie-attribute-list contains an attribute with an attribute-name of "Expires" (and does not contain an @@ -1335,90 +1412,90 @@ attribute in the cookie-attribute-list with an attribute- name of "Expires". Otherwise: 1. Set the cookie's persistent-flag to false. 2. Set the cookie's expiry-time to the latest representable date. - 5. If the cookie-attribute-list contains an attribute with an + 6. If the cookie-attribute-list contains an attribute with an attribute-name of "Domain": 1. Let the domain-attribute be the attribute-value of the last attribute in the cookie-attribute-list with an attribute- name of "Domain". Otherwise: 1. Let the domain-attribute be the empty string. - 6. If the user agent is configured to reject "public suffixes" and + 7. If the user agent is configured to reject "public suffixes" and the domain-attribute is a public suffix: 1. If the domain-attribute is identical to the canonicalized request-host: 1. Let the domain-attribute be the empty string. Otherwise: 1. Ignore the cookie entirely and abort these steps. NOTE: This step prevents "attacker.example" from disrupting the integrity of "site.example" by setting a cookie with a Domain attribute of "example". - 7. If the domain-attribute is non-empty: + 8. If the domain-attribute is non-empty: 1. If the canonicalized request-host does not domain-match the domain-attribute: 1. Ignore the cookie entirely and abort these steps. Otherwise: 1. Set the cookie's host-only-flag to false. 2. Set the cookie's domain to the domain-attribute. Otherwise: 1. Set the cookie's host-only-flag to true. 2. Set the cookie's domain to the canonicalized request-host. - 8. If the cookie-attribute-list contains an attribute with an + 9. If the cookie-attribute-list contains an attribute with an attribute-name of "Path", set the cookie's path to attribute- value of the last attribute in the cookie-attribute-list with an attribute-name of "Path". Otherwise, set the cookie's path to the default-path of the request-uri. - 9. If the cookie-attribute-list contains an attribute with an + 10. If the cookie-attribute-list contains an attribute with an attribute-name of "Secure", set the cookie's secure-only-flag to true. Otherwise, set the cookie's secure-only-flag to false. - 10. If the scheme component of the request-uri does not denote a + 11. If the scheme component of the request-uri does not denote a "secure" protocol (as defined by the user agent), and the cookie's secure-only-flag is true, then abort these steps and ignore the cookie entirely. - 11. If the cookie-attribute-list contains an attribute with an + 12. If the cookie-attribute-list contains an attribute with an attribute-name of "HttpOnly", set the cookie's http-only-flag to true. Otherwise, set the cookie's http-only-flag to false. - 12. If the cookie was received from a "non-HTTP" API and the + 13. If the cookie was received from a "non-HTTP" API and the cookie's http-only-flag is true, abort these steps and ignore the cookie entirely. - 13. If the cookie's secure-only-flag is false, and the scheme + 14. If the cookie's secure-only-flag is false, and the scheme component of request-uri does not denote a "secure" protocol, then abort these steps and ignore the cookie entirely if the cookie store contains one or more cookies that meet all of the following criteria: 1. Their name matches the name of the newly-created cookie. 2. Their secure-only-flag is true. 3. Their domain domain-matches the domain of the newly-created @@ -1428,28 +1505,28 @@ of the existing cookie. Note: The path comparison is not symmetric, ensuring only that a newly-created, non-secure cookie does not overlay an existing secure cookie, providing some mitigation against cookie-fixing attacks. That is, given an existing secure cookie named 'a' with a path of '/login', a non-secure cookie named 'a' could be set for a path of '/' or '/foo', but not for a path of '/login' or '/login/en'. - 14. If the cookie-attribute-list contains an attribute with an + 15. If the cookie-attribute-list contains an attribute with an attribute-name of "SameSite", and an attribute-value of "Strict", "Lax", or "None", set the cookie's same-site-flag to the attribute-value of the last attribute in the cookie- attribute-list with an attribute-name of "SameSite". Otherwise, set the cookie's same-site-flag to "Default". - 15. If the cookie's "same-site-flag" is not "None": + 16. If the cookie's "same-site-flag" is not "None": 1. If the cookie was received from a "non-HTTP" API, and the API was called from a browsing context's active document whose "site for cookies" is not same-site with the top-level origin, then abort these steps and ignore the newly created cookie entirely. 2. If the cookie was received from a "same-site" request (as defined in Section 5.2), skip the remaining substeps and continue processing the cookie. @@ -1462,57 +1539,57 @@ processing the cookie. Note: Top-level navigations can create a cookie with any "SameSite" value, even if the new cookie wouldn't have been sent along with the request had it already existed prior to the navigation. 4. Abort these steps and ignore the newly created cookie entirely. - 16. If the cookie's "same-site-flag" is "None", abort these steps + 17. If the cookie's "same-site-flag" is "None", abort these steps and ignore the cookie entirely unless the cookie's secure-only- flag is true. - 17. If the cookie-name begins with a case-sensitive match for the + 18. If the cookie-name begins with a case-sensitive match for the string "__Secure-", abort these steps and ignore the cookie entirely unless the cookie's secure-only-flag is true. - 18. If the cookie-name begins with a case-sensitive match for the + 19. If the cookie-name begins with a case-sensitive match for the string "__Host-", abort these steps and ignore the cookie entirely unless the cookie meets all the following criteria: 1. The cookie's secure-only-flag is true. 2. The cookie's host-only-flag is true. 3. The cookie-attribute-list contains an attribute with an attribute-name of "Path", and the cookie's path is "/". - 19. If the cookie store contains a cookie with the same name, + 20. If the cookie store contains a cookie with the same name, domain, host-only-flag, and path as the newly-created cookie: 1. Let old-cookie be the existing cookie with the same name, domain, host-only-flag, and path as the newly-created cookie. (Notice that this algorithm maintains the invariant that there is at most one such cookie.) 2. If the newly-created cookie was received from a "non-HTTP" API and the old-cookie's http-only-flag is true, abort these steps and ignore the newly created cookie entirely. 3. Update the creation-time of the newly-created cookie to match the creation-time of the old-cookie. 4. Remove the old-cookie from the cookie store. - 20. Insert the newly-created cookie into the cookie store. + 21. Insert the newly-created cookie into the cookie store. A cookie is "expired" if the cookie has an expiry date in the past. The user agent MUST evict all expired cookies from the cookie store if, at any time, an expired cookie exists in the cookie store. At any time, the user agent MAY "remove excess cookies" from the cookie store if the number of cookies sharing a domain field exceeds some implementation-defined upper bound (such as 50 cookies). @@ -1533,79 +1610,116 @@ 4. All cookies. If two cookies have the same removal priority, the user agent MUST evict the cookie with the earliest last-access-time first. When "the current session is over" (as defined by the user agent), the user agent MUST remove from the cookie store all cookies with the persistent-flag set to false. -5.5. The Cookie Header +5.6. Retrieval Model + + This section defines how cookies are retrieved from a cookie store in + the form of a cookie-string. A "retrieval" is any event which + requires generating a cookie-string. For example, a retrieval may + occur in order to build a Cookie header field for an HTTP request, or + may be required in order to return a cookie-string from a call to a + "non-HTTP" API that provides access to cookies. A retrieval has an + associated URI, same-site status, and type, which are defined below + depending on the type of retrieval. + +5.6.1. The Cookie Header Field The user agent includes stored cookies in the Cookie HTTP request - header. + header field. When the user agent generates an HTTP request, the user agent MUST NOT attach more than one Cookie header field. - A user agent MAY omit the Cookie header in its entirety. For + A user agent MAY omit the Cookie header field in its entirety. For example, the user agent might wish to block sending cookies during "third-party" requests from setting cookies (see Section 7.1). If the user agent does attach a Cookie header field to an HTTP - request, the user agent MUST send the cookie-string (defined below) - as the value of the header field. + request, the user agent MUST compute the cookie-string following the + algorithm defined in Section 5.6.3, where the retrieval's URI is the + request-uri, the retrieval's same-site status is computed for the + HTTP request as defined in Section 5.2, and the retrieval's type is + "HTTP". - The user agent MUST use an algorithm equivalent to the following - algorithm to compute the cookie-string from a cookie store and a - request-uri: +5.6.2. Non-HTTP APIs + + The user agent MAY implement "non-HTTP" APIs that can be used to + access stored cookies. + + A user agent MAY return an empty cookie-string in certain contexts, + such as when a retrieval occurs within a third-party context (see + Section 7.1). + + If a user agent does return cookies for a given call to a "non-HTTP" + API with an associated Document, then the user agent MUST compute the + cookie-string following the algorithm defined in Section 5.6.3, where + the retrieval's URI is defined by the caller (see + [DOM-DOCUMENT-COOKIE]), the retrieval's same-site status is "same- + site" if the Document's "site for cookies" is same-site with the top- + level origin as defined in Section 5.2.1 (otherwise it is "cross- + site"), and the retrieval's type is "non-HTTP". + +5.6.3. Retrieval Algorithm + + Given a cookie store and a retrieval, the following algorithm returns + a cookie-string from a given cookie store. 1. Let cookie-list be the set of cookies from the cookie store that meets all of the following requirements: * Either: - The cookie's host-only-flag is true and the canonicalized - request-host is identical to the cookie's domain. + host of the retrieval's URI is identical to the cookie's + domain. Or: - The cookie's host-only-flag is false and the canonicalized - request-host domain-matches the cookie's domain. + host of the retrieval's URI domain-matches the cookie's + domain. - * The request-uri's path path-matches the cookie's path. + * The retrieval's URI's path path-matches the cookie's path. - * If the cookie's secure-only-flag is true, then the request- - uri's scheme must denote a "secure" protocol (as defined by + * If the cookie's secure-only-flag is true, then the retrieval's + URI's scheme must denote a "secure" protocol (as defined by the user agent). NOTE: The notion of a "secure" protocol is not defined by this document. Typically, user agents consider a protocol secure if the protocol makes use of transport-layer security, such as SSL or TLS. For example, most user agents consider "https" to be a scheme that denotes a secure protocol. * If the cookie's http-only-flag is true, then exclude the - cookie if the cookie-string is being generated for a "non- - HTTP" API (as defined by the user agent). + cookie if the retrieval's type is "non-HTTP". - * If the cookie's same-site-flag is not "None", and the HTTP - request is cross-site (as defined in Section 5.2) then exclude - the cookie unless all of the following statements hold: + * If the cookie's same-site-flag is not "None" and the + retrieval's same-site status is "cross-site", then exclude the + cookie unless all of the following conditions are met: - 1. The same-site-flag is "Lax" or "Default". + - The retrieval's type is "HTTP". - 2. The HTTP request's method is "safe". + - The same-site-flag is "Lax" or "Default". - 3. The HTTP request's target browsing context is a top-level - browsing context. + - The HTTP request associated with the retrieval uses a + "safe" method. + + - The target browsing context of the HTTP request associated + with the retrieval is a top-level browsing context. 2. The user agent SHOULD sort the cookie-list in the following order: * Cookies with longer paths are listed before cookies with shorter paths. * Among cookies that have equal-length path fields, cookies with earlier creation-times are listed before cookies with later creation-times. @@ -1648,35 +1762,36 @@ * At least 4096 bytes per cookie (as measured by the sum of the length of the cookie's name, value, and attributes). * At least 50 cookies per domain. * At least 3000 cookies total. Servers SHOULD use as few and as small cookies as possible to avoid reaching these implementation limits and to minimize network - bandwidth due to the Cookie header being included in every request. + bandwidth due to the Cookie header field being included in every + request. Servers SHOULD gracefully degrade if the user agent fails to return - one or more cookies in the Cookie header because the user agent might - evict any cookie at any time on orders from the user. + one or more cookies in the Cookie header field because the user agent + might evict any cookie at any time on orders from the user. 6.2. Application Programming Interfaces - One reason the Cookie and Set-Cookie headers use such esoteric syntax - is that many platforms (both in servers and user agents) provide a - string-based application programming interface (API) to cookies, - requiring application-layer programmers to generate and parse the - syntax used by the Cookie and Set-Cookie headers, which many - programmers have done incorrectly, resulting in interoperability - problems. + One reason the Cookie and Set-Cookie header fields use such esoteric + syntax is that many platforms (both in servers and user agents) + provide a string-based application programming interface (API) to + cookies, requiring application-layer programmers to generate and + parse the syntax used by the Cookie and Set-Cookie header fields, + which many programmers have done incorrectly, resulting in + interoperability problems. Instead of providing string-based APIs to cookies, platforms would be well-served by providing more semantic APIs. It is beyond the scope of this document to recommend specific API designs, but there are clear benefits to accepting an abstract "Date" object instead of a serialized date string. 6.3. IDNA Dependency and Migration IDNA2008 [RFC5890] supersedes IDNA2003 [RFC3490]. However, there are @@ -1707,63 +1822,75 @@ from other servers (such as advertising networks). These third-party servers can use cookies to track the user even if the user never visits the server directly. For example, if a user visits a site that contains content from a third party and then later visits another site that contains content from the same third party, the third party can track the user between the two sites. Given this risk to user privacy, some user agents restrict how third- party cookies behave, and those restrictions vary widly. For instance, user agents might block third-party cookies entirely by - refusing to send Cookie headers or process Set-Cookie headers during - third-party requests. They might take a less draconian approach by - partitioning cookies based on the first-party context, sending one - set of cookies to a given third party in one first-party context, and - another to the same third party in another. + refusing to send Cookie header fields or process Set-Cookie header + fields during third-party requests. They might take a less draconian + approach by partitioning cookies based on the first-party context, + sending one set of cookies to a given third party in one first-party + context, and another to the same third party in another. This document grants user agents wide latitude to experiment with third-party cookie policies that balance the privacy and compatibility needs of their users. However, this document does not endorse any particular third-party cookie policy. Third-party cookie blocking policies are often ineffective at achieving their privacy goals if servers attempt to work around their restrictions to track users. In particular, two collaborating servers can often track users without using cookies at all by injecting identifying information into dynamic URLs. -7.2. User Controls +7.2. Cookie policy + + User agents MAY enforce a cookie policy consisting of restrictions on + how cookies may be used or ignored (see Section 5.3). + + A cookie policy may govern which domains or parties, as in first and + third parties (see Section 7.1), for which the user agent will allow + cookie access. The policy can also define limits on cookie size, + cookie expiry, and the number of cookies per domain or in total. + + The goal of a restrictive cookie policy is often to improve security + or privacy. User agents often allow users to change the cookie + policy (see Section 7.3). + +7.3. User Controls User agents SHOULD provide users with a mechanism for managing the cookies stored in the cookie store. For example, a user agent might let users delete all cookies received during a specified time period or all the cookies related to a particular domain. In addition, many user agents include a user interface element that lets users examine the cookies stored in their cookie store. User agents SHOULD provide users with a mechanism for disabling cookies. When cookies are disabled, the user agent MUST NOT include - a Cookie header in outbound HTTP requests and the user agent MUST NOT - process Set-Cookie headers in inbound HTTP responses. + a Cookie header field in outbound HTTP requests and the user agent + MUST NOT process Set-Cookie header fields in inbound HTTP responses. - Some user agents provide users the option of preventing persistent + User agents MAY offer a way to change the cookie policy (see + Section 7.2). + + User agents MAY provide users the option of preventing persistent storage of cookies across sessions. When configured thusly, user agents MUST treat all received cookies as if the persistent-flag were set to false. Some popular user agents expose this functionality via "private browsing" mode [Aggarwal2010]. - Some user agents provide users with the ability to approve individual - writes to the cookie store. In many common usage scenarios, these - controls generate a large number of prompts. However, some privacy- - conscious users find these controls useful nonetheless. - -7.3. Expiration Dates +7.4. Expiration Dates Although servers can set the expiration date for cookies to the distant future, most user agents do not actually retain cookies for multiple decades. Rather than choosing gratuitously long expiration periods, servers SHOULD promote user privacy by selecting reasonable cookie expiration periods based on the purpose of the cookie. For example, a typical session identifier might reasonably be set to expire in two weeks. 8. Security Considerations @@ -1811,41 +1938,41 @@ wish to consider entangling designation and authorization by treating URLs as capabilities. Instead of storing secrets in cookies, this approach stores secrets in URLs, requiring the remote entity to supply the secret itself. Although this approach is not a panacea, judicious application of these principles can lead to more robust security. 8.3. Clear Text Unless sent over a secure channel (such as TLS), the information in - the Cookie and Set-Cookie headers is transmitted in the clear. + the Cookie and Set-Cookie header fields is transmitted in the clear. - 1. All sensitive information conveyed in these headers is exposed to - an eavesdropper. + 1. All sensitive information conveyed in these header fields is + exposed to an eavesdropper. - 2. A malicious intermediary could alter the headers as they travel - in either direction, with unpredictable results. + 2. A malicious intermediary could alter the header fields as they + travel in either direction, with unpredictable results. - 3. A malicious client could alter the Cookie header before + 3. A malicious client could alter the Cookie header fields before transmission, with unpredictable results. Servers SHOULD encrypt and sign the contents of cookies (using whatever format the server desires) when transmitting them to the user agent (even when sending the cookies over a secure channel). However, encrypting and signing cookie contents does not prevent an attacker from transplanting a cookie from one user agent to another or from replaying the cookie at a later time. In addition to encrypting and signing the contents of every cookie, servers that require a higher level of security SHOULD use the Cookie - and Set-Cookie headers only over a secure channel. When using + and Set-Cookie header fields only over a secure channel. When using cookies over a secure channel, servers SHOULD set the Secure attribute (see Section 4.1.2.5) for every cookie. If a server does not set the Secure attribute, the protection provided by the secure channel will be largely moot. For example, consider a webmail server that stores a session identifier in a cookie and is typically accessed over HTTPS. If the server does not set the Secure attribute on its cookies, an active network attacker can intercept any outbound HTTP request from the user agent and redirect that request to the webmail server over HTTP. @@ -1917,37 +2044,37 @@ their subdomains). For example, consider foo.site.example and bar.site.example. The foo.site.example server can set a cookie with a Domain attribute of "site.example" (possibly overwriting an existing "site.example" cookie set by bar.site.example), and the user agent will include that cookie in HTTP requests to bar.site.example. In the worst case, bar.site.example will be unable to distinguish this cookie from a cookie it set itself. The foo.site.example server might be able to leverage this ability to mount an attack against bar.site.example. - Even though the Set-Cookie header supports the Path attribute, the - Path attribute does not provide any integrity protection because the - user agent will accept an arbitrary Path attribute in a Set-Cookie - header. For example, an HTTP response to a request for + Even though the Set-Cookie header field supports the Path attribute, + the Path attribute does not provide any integrity protection because + the user agent will accept an arbitrary Path attribute in a Set- + Cookie header field. For example, an HTTP response to a request for http://site.example/foo/bar can set a cookie with a Path attribute of "/qux". Consequently, servers SHOULD NOT both run mutually distrusting services on different paths of the same host and use cookies to store security-sensitive information. An active network attacker can also inject cookies into the Cookie - header sent to https://site.example/ by impersonating a response from - http://site.example/ and injecting a Set-Cookie header. The HTTPS - server at site.example will be unable to distinguish these cookies - from cookies that it set itself in an HTTPS response. An active - network attacker might be able to leverage this ability to mount an - attack against site.example even if site.example uses HTTPS - exclusively. + header field sent to https://site.example/ by impersonating a + response from http://site.example/ and injecting a Set-Cookie header + field. The HTTPS server at site.example will be unable to + distinguish these cookies from cookies that it set itself in an HTTPS + response. An active network attacker might be able to leverage this + ability to mount an attack against site.example even if site.example + uses HTTPS exclusively. Servers can partially mitigate these attacks by encrypting and signing the contents of their cookies. However, using cryptography does not mitigate the issue completely because an attacker can replay a cookie he or she received from the authentic site.example server in the user's session, with unpredictable results. Finally, an attacker might be able to force the user agent to delete cookies by storing a large number of cookies. Once the user agent reaches its storage limit, the user agent will be forced to evict @@ -1983,114 +2111,181 @@ Setting the "SameSite" attribute in "strict" mode provides robust defense in depth against CSRF attacks, but has the potential to confuse users unless sites' developers carefully ensure that their cookie-based session management systems deal reasonably well with top-level navigations. Consider the scenario in which a user reads their email at MegaCorp Inc's webmail provider "https://site.example/". They might expect that clicking on an emailed link to "https://projects.example/secret/ project" would show them the secret project that they're authorized - to see, but if "projects.example" has marked their session cookies as - "SameSite", then this cross-site navigation won't send them along - with the request. "projects.example" will render a 404 error to avoid - leaking secret information, and the user will be quite confused. + to see, but if "https://projects.example" has marked their session + cookies as "SameSite=Strict", then this cross-site navigation won't + send them along with the request. "https://projects.example" will + render a 404 error to avoid leaking secret information, and the user + will be quite confused. Developers can avoid this confusion by adopting a session management system that relies on not one, but two cookies: one conceptually granting "read" access, another granting "write" access. The latter - could be marked as "SameSite", and its absence would prompt a + could be marked as "SameSite=Strict", and its absence would prompt a reauthentication step before executing any non-idempotent action. - The former could drop the "SameSite" attribute entirely, or choose - the "Lax" version of enforcement, in order to allow users access to - data via top-level navigation. + The former could be marked as "SameSite=Lax", in order to allow users + access to data via top-level navigation, or "SameSite=None", to + permit access in all contexts (including cross-site embedded + contexts). 8.8.3. Mashups and Widgets - The "SameSite" attribute is inappropriate for some important use- - cases. In particular, note that content intended for embedding in a - cross-site contexts (social networking widgets or commenting - services, for instance) will not have access to same-site cookies. - Cookies may be required for requests triggered in these cross-site - contexts in order to provide seamless functionality that relies on a - user's state. + The "Lax" and "Strict" values for the "SameSite" attribute are + inappropriate for some important use-cases. In particular, note that + content intended for embedding in cross-site contexts (social + networking widgets or commenting services, for instance) will not + have access to same-site cookies. Cookies which are required in + these situations should be marked with "SameSite=None" to allow + access in cross-site contexts. Likewise, some forms of Single-Sign-On might require cookie-based authentication in a cross-site context; these mechanisms will not - function as intended with same-site cookies. + function as intended with same-site cookies and will also require + "SameSite=None". 8.8.4. Server-controlled SameSite cookies in and of themselves don't do anything to address the general privacy concerns outlined in Section 7.1 of [RFC6265]. The "SameSite" attribute is set by the server, and serves to mitigate the risk of certain kinds of attacks that the server is worried about. The user is not involved in this decision. Moreover, a number of side-channels exist which could allow a server to link distinct requests even in the absence of cookies (for example, connection and/or socket pooling between same-site and cross-site requests). -9. IANA Considerations +8.8.5. Reload navigations + Requests issued for reloads triggered through user interface elements + (such as a refresh button on a toolbar) are same-site only if the + reloaded document was originally navigated to via a same-site + request. This differs from the handling of other reload navigations, + which are always same-site if top-level, since the source browsing + context's active document is precisely the document being reloaded. + + This special handling of reloads triggered through a user interface + element avoids sending "SameSite" cookies on user-initiated reloads + if they were withheld on the original navigation (i.e., if the + initial navigation were cross-site). If the reload navigation were + instead considered same-site, and sent all the initially withheld + "SameSite" cookies, the security benefits of withholding the cookies + in the first place would be nullified. This is especially important + given that the absence of "SameSite" cookies withheld on a cross-site + navigation request may lead to visible site breakage, prompting the + user to trigger a reload. + + For example, suppose the user clicks on a link from + "https://attacker.example/" to "https://victim.example/". This is a + cross-site request, so "SameSite=Strict" cookies are withheld. + Suppose this causes "https://victim.example/" to appear broken, + because the site only displays its sensitive content if a particular + "SameSite" cookie is present in the request. The user, frustrated by + the unexpectedly broken site, presses refresh on their browser's + toolbar. To now consider the reload request same-site and send the + initially withheld "SameSite" cookie would defeat the purpose of + withholding it in the first place, as the reload navigation triggered + through the user interface may replay the original (potentially + malicious) request. Thus, the reload request should be considered + cross-site, like the request that initially navigated to the page. + +8.8.6. Top-level requests with "unsafe" methods + + The "Lax" enforcement mode described in Section 5.4.7.1 allows a + cookie to be sent with a cross-site HTTP request if and only if it is + a top-level navigation with a "safe" HTTP method. Implementation + experience shows that this is difficult to apply as the default + behavior, as some sites may rely on cookies not explicitly specifying + a "SameSite" attribute being included on top-level cross-site + requests with "unsafe" HTTP methods (as was the case prior to the + introduction of the "SameSite" attribute). + + For example, a login flow may involve a cross-site top-level "POST" + request to an endpoint which expects a cookie with login information. + For such a cookie, "Lax" enforcement is not appropriate, as it would + cause the cookie to be excluded due to the unsafe HTTP request + method. On the other hand, "None" enforcement would allow the cookie + to be sent with all cross-site requests, which may not be desirable + due to the cookie's sensitive contents. + + The "Lax-allowing-unsafe" enforcement mode described in + Section 5.4.7.2 retains some of the protections of "Lax" enforcement + (as compared to "None") while still allowing cookies to be sent + cross-site with unsafe top-level requests. + + As a more permissive variant of "Lax" mode, "Lax-allowing-unsafe" + mode necessarily provides fewer protections against CSRF. + Ultimately, the provision of such an enforcement mode should be seen + as a temporary, transitional measure to ease adoption of "Lax" + enforcement by default. + +9. IANA Considerations 9.1. Cookie The permanent message header field registry (see [RFC3864]) needs to be updated with the following registration: Header field name: Cookie Applicable protocol: http Status: standard Author/Change controller: IETF - Specification document: this specification (Section 5.5) + Specification document: this specification (Section 5.6.1) 9.2. Set-Cookie The permanent message header field registry (see [RFC3864]) needs to be updated with the following registration: Header field name: Set-Cookie Applicable protocol: http Status: standard Author/Change controller: IETF - Specification document: this specification (Section 5.3) + Specification document: this specification (Section 5.4) 9.3. Cookie Attribute Registry - The "Cookie Attribute Registry" defines the name space of attribute - used to control cookies' behavior. The registry is maintained at - https://www.iana.org/assignments/cookie-attribute-names - (https://www.iana.org/assignments/cookie-attribute-names). + IANA is requested to create the "Cookie Attribute Registry", defining + the name space of attribute used to control cookies' behavior. The + registry should be maintained at https://www.iana.org/assignments/ + cookie-attribute-names (https://www.iana.org/assignments/cookie- + attribute-names). 9.3.1. Procedure Each registered attribute name is associated with a description, and a reference detailing how the attribute is to be processed and stored. New registrations happen on a "RFC Required" basis (see Section 4.7 of [RFC8126]). The attribute to be registered MUST match the "extension-av" syntax defined in Section 4.1.1. Note that attribute names are generally defined in CamelCase, but technically accepted case-insensitively. 9.3.2. Registration - The "Cookie Attribute Registry" will be updated with the + The "Cookie Attribute Registry" should be created with the registrations below: +==========+==================================+ | Name | Reference | +==========+==================================+ | Domain | Section 4.1.2.3 of this document | +----------+----------------------------------+ | Expires | Section 4.1.2.1 of this document | +----------+----------------------------------+ | HttpOnly | Section 4.1.2.6 of this document | @@ -2103,80 +2298,83 @@ +----------+----------------------------------+ | Secure | Section 4.1.2.5 of this document | +----------+----------------------------------+ Table 1 10. References 10.1. Normative References + [DOM-DOCUMENT-COOKIE] + WHATWG, "HTML - Living Standard", 18 May 2021, + . + [FETCH] van Kesteren, A., "Fetch", n.d., . [HTML] Hickson, I., Pieters, S., van Kesteren, A., Jägenstedt, P., and D. Denicola, "HTML", n.d., . + [HTTPSEM] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP + Semantics", Work in Progress, Internet-Draft, draft-ietf- + httpbis-semantics-16, 27 May 2021, + . + [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, - . + . [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, DOI 10.17487/RFC1123, October 1989, - . + . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, - . + . [RFC3490] Costello, A., "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003, . See Section 6.3 for an explanation why the normative reference to an obsoleted specification is needed. [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet Application Protocol Collation Registry", RFC 4790, DOI 10.17487/RFC4790, March 2007, - . + . [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, - . + . [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, DOI 10.17487/RFC5890, August 2010, - . + . [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, DOI 10.17487/RFC6454, December 2011, - . - - [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer - Protocol (HTTP/1.1): Message Syntax and Routing", - RFC 7230, DOI 10.17487/RFC7230, June 2014, - . - - [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer - Protocol (HTTP/1.1): Semantics and Content", RFC 7231, - DOI 10.17487/RFC7231, June 2014, - . + . [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, - . + . + + [SAMESITE] WHATWG, "HTML - Living Standard", 26 January 2021, + . [SERVICE-WORKERS] Russell, A., Song, J., and J. Archibald, "Service Workers", n.d., . [USASCII] American National Standards Institute, "Coded Character Set -- 7-bit American Standard Code for Information Interchange", ANSI X3.4, 1986. 10.2. Informative References @@ -2200,77 +2398,77 @@ DOI 10.1145/1455770.1455782, ISBN 978-1-59593-810-7, ACM CCS '08: Proceedings of the 15th ACM conference on Computer and communications security (pages 75-88), October 2008, . [I-D.ietf-httpbis-cookie-alone] West, M., "Deprecate modification of 'secure' cookies from non-secure origins", Work in Progress, Internet-Draft, draft-ietf-httpbis-cookie-alone-01, 5 September 2016, - . + . [I-D.ietf-httpbis-cookie-prefixes] West, M., "Cookie Prefixes", Work in Progress, Internet- Draft, draft-ietf-httpbis-cookie-prefixes-00, 23 February - 2016, . + 2016, . [I-D.ietf-httpbis-cookie-same-site] West, M. and M. Goodwin, "Same-Site Cookies", Work in Progress, Internet-Draft, draft-ietf-httpbis-cookie-same- - site-00, 20 June 2016, . + site-00, 20 June 2016, . [prerendering] Bentzel, C., "Chrome Prerendering", n.d., . [PSL] "Public Suffix List", n.d., . [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000, - . + . [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November - 2003, . + 2003, . [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, DOI 10.17487/RFC3864, September 2004, - . + . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, - . + . [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, - . + . [RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008", RFC 5895, DOI 10.17487/RFC5895, September 2010, - . + . [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, DOI 10.17487/RFC6265, April 2011, - . + . [RFC7034] Ross, D. and T. Gondrom, "HTTP Header Field X-Frame- Options", RFC 7034, DOI 10.17487/RFC7034, October 2013, - . + . [UTS46] Davis, M. and M. Suignard, "Unicode IDNA Compatibility Processing", UNICODE Unicode Technical Standards # 46, June 2016, . Appendix A. Changes A.1. draft-ietf-httpbis-rfc6265bis-00 * Port [RFC6265] to Markdown. No (intentional) normative changes. @@ -2405,49 +2603,90 @@ * Fixed serialization for nameless/valueless cookies: https://github.com/httpwg/http-extensions/pull/1143 (https://github.com/httpwg/http-extensions/pull/1143). * Converted a normative reference to Mozilla's Public Suffix List [PSL] into an informative reference: https://github.com/httpwg/ http-extensions/issues/1159 (https://github.com/httpwg/http- extensions/issues/1159). A.8. draft-ietf-httpbis-rfc6265bis-07 + * Moved instruction to ignore cookies with empty cookie-name and - cookie-value from Section 5.3 to Section 5.4 to ensure that they + cookie-value from Section 5.4 to Section 5.5 to ensure that they apply to cookies created without parsing a cookie string: https://github.com/httpwg/http-extensions/issues/1234 (https://github.com/httpwg/http-extensions/issues/1234). * Add a default enforcement value to the "same-site-flag", equivalent to "SameSite=Lax": https://github.com/httpwg/http- extensions/pull/1325 (https://github.com/httpwg/http-extensions/ pull/1325). * Require a Secure attribute for "SameSite=None": https://github.com/httpwg/http-extensions/pull/1323 (https://github.com/httpwg/http-extensions/pull/1323). * Consider scheme when running the same-site algorithm: https://github.com/httpwg/http-extensions/pull/1324 (https://github.com/httpwg/http-extensions/pull/1324). +A.9. draft-ietf-httpbis-rfc6265bis-08 + + * Define "same-site" for reload navigation requests, e.g. those + triggered via user interface elements: https://github.com/httpwg/ + http-extensions/pull/1384 (https://github.com/httpwg/http- + extensions/pull/1384) + + * Consider redirects when defining same-site: + https://github.com/httpwg/http-extensions/pull/1348 + (https://github.com/httpwg/http-extensions/pull/1348) + + * Align on using HTML terminology for origins: + https://github.com/httpwg/http-extensions/pull/1416 + (https://github.com/httpwg/http-extensions/pull/1416) + + * Modify cookie parsing and creation algorithms in Section 5.4 and + Section 5.5 to explicitly handle control characters: + https://github.com/httpwg/http-extensions/pull/1420 + (https://github.com/httpwg/http-extensions/pull/1420) + + * Refactor cookie retrieval algorithm to support non-HTTP APIs: + https://github.com/httpwg/http-extensions/pull/1428 + (https://github.com/httpwg/http-extensions/pull/1428) + + * Define "Lax-allowing-unsafe" SameSite enforcement mode: + https://github.com/httpwg/http-extensions/pull/1435 + (https://github.com/httpwg/http-extensions/pull/1435) + + * Consistently use "header field" (vs 'header"): + https://github.com/httpwg/http-extensions/pull/1527 + (https://github.com/httpwg/http-extensions/pull/1527) + Acknowledgements - RFC 6265 was written by Adam Barth. This document is a minor update - of RFC 6265, adding small features, and aligning the specification - with the reality of today's deployments. Here, we're standing upon - the shoulders of a giant since the majority of the text is still - Adam's. + RFC 6265 was written by Adam Barth. This document is an update of + RFC 6265, adding features and aligning the specification with the + reality of today's deployments. Here, we're standing upon the + shoulders of a giant since the majority of the text is still Adam's. Authors' Addresses + Lily Chen (editor) + Google LLC + + Email: chlily@google.com + + Steven Englehardt (editor) + Mozilla + + Email: senglehardt@mozilla.com + Mike West (editor) - Google, Inc + Google LLC Email: mkwst@google.com URI: https://mikewest.org/ - John Wilander (editor) Apple, Inc Email: wilander@apple.com