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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 6652

MARF Working Group                                          S. Kitterman
Internet-Draft                                          Agari Data, Inc.
Intended status: Standards Track                        February 1, 2012
Expires: August 4, 2012


   SPF Authentication Failure Reporting using the Abuse Report Format
                    draft-ietf-marf-spf-reporting-05

Abstract

   This memo presents extensions to the Abuse Reporting Format (ARF),
   and Sender Policy Framework (SPF) specifications to allow for
   detailed reporting of message authentication failures in an on-demand
   fashion.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 4, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Keywords . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Imported Definitions . . . . . . . . . . . . . . . . . . .  4
   3.  Optional Reporting Address for SPF . . . . . . . . . . . . . .  5
   4.  Requested Reports  . . . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Requested Reports for SPF Failures . . . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  SPF Modifier Registration  . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     6.1.  Inherited Considerations . . . . . . . . . . . . . . . . .  9
     6.2.  Forgeries  . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.3.  Envelope Sender Selection  . . . . . . . . . . . . . . . .  9
     6.4.  Automatic Generation . . . . . . . . . . . . . . . . . . . 10
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 13
   Appendix B.  Examples  . . . . . . . . . . . . . . . . . . . . . . 14
     B.1.  Minimal SPF DNS record change to add a reporting
           address  . . . . . . . . . . . . . . . . . . . . . . . . . 14
     B.2.  SPF DNS record with reporting address, report
           percentage, and requested report type  . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15

























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1.  Introduction

   [ARF] defines a message format for sending reports of abuse in the
   messaging infrastructure, with an eye toward automating both the
   generating and consumption of those reports.

   [SPF] is one mechanism for message sender authentication; it is
   "path-based" meaning it authenticates the route that a message took
   from origin to destination.  As with other email authentication
   methods, like [DKIM], the output is a verified domain name that can
   then be subjected to some sort of evaluation process (e.g.,
   comparison to a known-good list, submission to a reputation service,
   etc.).

   Deployers of message sender authentication technologies are
   increasingly seeking visibility into DKIM verification failures,
   unauthorized path traversals (SPF failures), and conformance failures
   involving the published signing practices (e.g., [ADSP]) of an
   Administrative Mail Domain (ADMD; see [EMAIL-ARCH]).

   This document extends [SPF] to add an optional reporting address and
   other parameters.  Extension of [ARF] to add features required for
   the reporting of these incidents is covered in
   [I-D.MARF-AUTHFAILURE-REPORT].

   This document additionally creates a an IANA registry of [SPF] record
   modifiers to avoid modifier namespace collisions.
























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2.  Definitions

2.1.  Keywords

   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 [KEYWORDS].

2.2.  Imported Definitions

   The ABNF token "qp-section" is defined in [MIME].

   "local-part" is defined in [MAIL].

   "addr-spec" is defined in [MAIL].




































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3.  Optional Reporting Address for SPF

   There exist cases in which a domain name owner employing [SPF] for
   announcing sending practices may want to know when messages are
   received via unauthorized routing.  Currently there is no such method
   defined in conjunction with standardized approaches such as [ARF].
   Similar information can be gathered using a specially crafted [SPF]
   record and a special DNS server to track [SPF] record lookups.

   This document defines the following optional "modifier" (as defined
   in Section 4.6.1 of [SPF]) to SPF records, using the form defined in
   that specification:

   ra=  Reporting Address (plain-text; OPTIONAL; no default).  MUST be a
      local-part (see Section 3.4.1 of [MAIL]) specifying an e-mail
      address to which a report SHOULD be sent when mail claiming to be
      from this domain (see Section 2.4 of [SPF] for a description of
      how domains are identified for SPF checks) has failed the
      evaluation algorithm described in [SPF], in particular because a
      message arrived via an unauthorized route.  To generate a complete
      address to which the report is sent, the verifier simply appends
      to this value an "@" followed by the SPF domain per paragraph 4.1
      of [SPF]. r= modifiers in a record that was reached by following
      an include: mechanism MUST be ignored.

      ABNF:

      spf-report-tag = %x72.61 "=" qp-section

   rp=  Requested Report Percentage (plain-text; OPTIONAL; default is
      "100").  The value is an integer from 0 to 100 inclusive that
      indicates what percentage of incidents of signature authentication
      failures, selected at random, are to cause reports to be
      generated.  The report generator SHOULD NOT issue reports for more
      than the requested percentage of incidents.  Report generators MAY
      make use of the "Incidents:" field in [ARF] to indicate that there
      are more reportable incidents than there are reports.

      ABNF:

      spf-rp-tag = %x72.69 *WSP "=" *WSP 1*12DIGIT "/" 1*12DIGIT

   rr=  Requested Reports (plain-text; OPTIONAL; default is "all").  The
      value MUST be a colon-separated list of tokens representing those
      conditions under which a report is desired.  See Section 4.1 for a
      list of valid tags.





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      ABNF:

      spf-rr-type = ( "all" / "e" / "f" / "s" / "n" )

      spf-rr-tag = %x72.72 "=" spf-ro-type 0* ( ":" spf-rr-type )

   In the absence of an "ra=" tag in the SPF record, the "rp=" and "rr="
   tags MUST be ignored, and the report generator MUST NOT issue a
   report.










































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4.  Requested Reports

   This memo also includes, as the "ro" tokens defined above, the means
   by which the sender can request reports for specific circumstances of
   interest.  Verifiers MUST NOT generate reports for incidents that do
   not match a requested report, and MUST ignore requests for reports
   not included in this these lists.

4.1.  Requested Reports for SPF Failures

   The following report requests are defined for SPF results:

   all  All reports are requested.

   e  Reports are requested for messages that produced an SPF result of
      "TempError" or "PermError".

   f  Reports are requested for messages that produced an SPF result of
      "Fail".

   s  Reports are requested for messages that produced an SPF result of
      "SoftFail".

   n  Reports are requested for messages that produced an SPF result of
      "Neutral" or "None".


























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5.  IANA Considerations

   As required by [IANA-CONSIDERATIONS], this section contains registry
   information for the new [SPF] modifiers.

5.1.  SPF Modifier Registration

   IANA is requested to create the Sender Policy Framework Modifier
   Registry, to include a list of all registered SPF modifier names and
   their defining documents.

   New registrations or updates MUST be published in accordance with the
   "Specification Required" guidelines as described in
   [IANA-CONSIDERATIONS].  New registrations and updates MUST contain
   the following information:

   1.  Name of the modifier being registered or updated

   2.  The document in which the specification of the modifier is
       published

   3.  New or updated status, which MUST be one of:

       current:  The field is in current use

       deprecated:  The field is in current use but its use is
          discouraged

       historic:  The field is no longer in current use

   An update may make a notation on an existing registration indicating
   that a registered field is historic or deprecated if appropriate.

                 +------------+-----------------+---------+
                 | MODIFIER   | REFERENCE       | STATUS  |
                 +------------+-----------------+---------+
                 | exp        | RFC4408         | current |
                 | redirect   | RFC4408         | current |
                 | ra         | (this document) | current |
                 | rp         | (this document) | current |
                 | rr         | (this document) | current |
                 +------------+-----------------+---------+









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6.  Security Considerations

   Security issues with respect to these reports are similar to those
   found in [DSN].

6.1.  Inherited Considerations

   Implementors are advised to consider the Security Considerations
   sections of [SPF], [ARF], and [I-D.MARF-AUTHFAILURE-REPORT].

6.2.  Forgeries

   These reports may be forged as easily as ordinary Internet electronic
   mail.  User agents and automatic mail handling facilities (such as
   mail distribution list exploders) that wish to make automatic use of
   reports of any kind should take appropriate precautions to minimize
   the potential damage from denial-of-service attacks.

   Security threats related to forged reports include the sending of:

   a.  A falsified authentication failure notification when the message
       was in fact delivered to the indicated recipient;

   b.  Falsified result information, such as [SPF] result type, domain,
       etc.

   Perhaps the simplest means of mitigating this threat is to assert
   that these reports should themselves pass [SPF] checks and/or use
   other email authentication technologies such as [DKIM].

6.3.  Envelope Sender Selection

   In the case of transmitted reports in the form of a new message
   (versus rejections during an [SMTP] session), it is necessary to
   construct the message so as to avoid amplification attacks,
   deliberate or otherwise.  The envelope sender address of the report
   MUST be chosen so that these reports will not generate mail loops.
   These types of reports MUST not be generated for [ARF] messages.

   Similar to Section 2 of [DSN], the envelope sender address of the
   report SHOULD be chosen to ensure that no feed back reports will be
   issued in response to the report itself.

   When an [SMTP] transaction is used to send a report, the MAIL FROM
   command MUST either use the NULL return address, i.e., "MAIL
   FROM:<>", or one that will pass [SPF] MAIL FROM checks on receipt.
   The HELO/EHLO command SHOULD also be selected so that it will pass
   [SPF] HELO checks.



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6.4.  Automatic Generation

   Automatic generation of these reports by checking agents can cause a
   denial-of-service attack when a large volume of e-mail is sent that
   causes authentication failures for whatever reason.

   Limiting the rate of generation of these messages may be appropriate
   but threatens to inhibit the distribution of important and possibly
   time-sensitive information.  The spf-rp-tag provides a mechanism to
   communicate appropriate limits.

   Other rate limiting provisions might be considered, including
   detection of a temporary failure response from the report destination
   and thus halting report generation to that destination for some
   period, or simply imposing or negotiating a hard limit on the number
   of reports to be sent to a particular receiver in a given time frame.



































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7.  References

7.1.  Normative References

   [ARF]      Shafranovich, Y., Levine, J., and M. Kucherawy, "An
              Extensible Format for Email Feedback Reports", RFC 5965,
              August 2010.

   [EMAIL-ARCH]
              Crocker, D., "Internet Mail Architecture", RFC 5598,
              October 2008.

   [I-D.MARF-AUTHFAILURE-REPORT]
              Fontana, H., "Authentication Failure Reporting using the
              Abuse Report Format", January 2012.

   [IANA-CONSIDERATIONS]
              Alvestrand, H. and T. Narten, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226, May 2008.

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [MAIL]     Resnick, P., "Internet Message Format", RFC 5322,
              October 2008.

   [MIME]     Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [SMTP]     Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [SPF]      Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
              for Authorizing Use of Domains in E-Mail, Version 1",
              RFC 4408, April 2006.

7.2.  Informative References

   [ADSP]     Allman, E., Delany, M., Fenton, J., and J. Levine, "DKIM
              Sender Signing Practises", RFC 5617, August 2009.

   [DKIM]     Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
              J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
              Signatures", RFC 4871, May 2007.

   [DSN]      Moore, K. and G. Vaudreuil, "An Extensible Message Format



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              for Delivery Status Notifications", RFC 3464,
              January 2003.

















































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Appendix A.  Acknowledgements

   The author wishes to acknowledge the following for their review and
   constructive criticism of this proposal: Murray Kucherawy, Tim
   Draegen, Julian Mehnle, and John Levine.














































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Appendix B.  Examples

B.1.  Minimal SPF DNS record change to add a reporting address

   v=spf1 mx:example.org ra=postmaster -all

B.2.  SPF DNS record with reporting address, report percentage, and
      requested report type

   v=spf1 mx:example.org -all ra=postmaster rp=10 rr=e









































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Author's Address

   Scott Kitterman
   Agari Data, Inc.
   3611 Scheel Dr
   Ellicott City, MD  21042
   US

   Phone: +1 301 325 5475
   Email: skitterman@agari.com









































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