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MARF Working Group                                          S. Kitterman
Internet-Draft                                    Authentication Metrics
Intended status: Standards Track                        October 24, 2011
Expires: April 26, 2012


   SPF Authentication Failure Reporting using the Abuse Report Format
                    draft-ietf-marf-spf-reporting-02

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 April 26, 2012.

Copyright Notice

   Copyright (c) 2011 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.  Reports From Unrelated Domains . . . . . . . . . . . . . .  9
     6.3.  Envelope Sender Selection  . . . . . . . . . . . . . . . .  9
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 12
   Appendix B.  Examples  . . . . . . . . . . . . . . . . . . . . . . 13
     B.1.  Minimal SPF DNS record change to add a reporting
           address  . . . . . . . . . . . . . . . . . . . . . . . . . 13
     B.2.  SPF DNS record with reporting address, report
           interval, and requested report type  . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14


























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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
   an optional means of specifying a desired report format 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 practises 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:

   r= Reporting Address (plain-text; OPTIONAL; no default).  MUST be a
      local-part or addr-spec (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.  The format
      of this reply MUST be in the format specified by the "rf=" tag
      defined below.  If only a local-part is provided, then 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 "=" qp-section

   rf=  Reporting Format (plain-text; OPTIONAL; default is "arf").  The
      value MUST be a colon-separated list of tokens representing
      desired reporting formats in decreasing order of preference.  Each
      element of the list MUST be a token that is taken from the
      registered list of report formats.  See
      [I-D.MARF-AUTHFAILURE-REPORT] for a description of recognized
      formats.  The verifier generating reports SHOULD generate a report
      using the first token in the list that represents a report format
      it is capable of generating.  If no supported formats are
      requested, then a report MUST not be sent.

      ABNF:

      spf-rf-tag = %x72 %x66 "=" rep-format 0*( ":" rep-format )






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   ri=  Requested Report Interval (plain-text; OPTIONAL; default is
      "0").  The value is an unsigned 32-bit integer that specifies the
      number of incidents for which to skip reports, i.e. for a value of
      "1", every other report about a given type of incident (e.g.  SPF
      related) should be skipped.  A value of "0" requests a report for
      every incident.  Where the requested interval is not zero, the
      agent generating a report SHOULD include an "Incidents:" field in
      the generated report so the receiving agent has some indication of
      how many reports were suppressed.

      ABNF:

      spf-ri-tag = %x72 %x69 "=" 1*DIGIT

   ro=  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.

      ABNF:

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

      spf-ro-tag = %x72 %x6f "=" spf-ro-type 0* ( ":" spf-ro-type )

   In the absence of an 'r=' tag in the SPF record, all other fields
   defined above MUST be ignored.
























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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".





























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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 |
                 | r          | (this document) | current |
                 | rf         | (this document) | current |
                 | ri         | (this document) | current |
                 | ro         | (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.  Reports From Unrelated Domains

   SPF records can be used by other domains via include mechanisms and
   redirect modifiers.  If reporting addresses included in these records
   are specified with a full addr-spec then reports for other,
   potentially unrelated, domains may be reported to this address.  In
   theory, malicious senders might use this as a path for generating
   large numbers of feedback reports.  To mitigate this issue, specify
   reporting addresses with a local-part so that reports will be
   directed to the original domain from which the message causing the
   feedback report was sent.

6.3.  Envelope Sender Selection

   In the case of transmitted reports in the form of a new message, it
   is necessary to construct the message so as to avoid amplification
   attacks, deliberate or otherwise.  Thus, per Section 2 of [DSN], the
   envelope sender address of the report SHOULD be chosen to ensure that
   no delivery status reports will be issued in response to the report
   itself, and MUST be chosen so that these reports will not generate
   mail loops.  Whenever an [SMTP] transaction is used to send a report,
   the MAIL FROM command MUST use a NULL return address, i.e.  "MAIL
   FROM:<>".  The HELO/EHLO command SHOULD pass [SPF] HELO checks.


















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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", June 2011.

   [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, and Julian Mehnle.














































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Appendix B.  Examples

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

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

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

   v=spf1 mx:example.org -all r=postmaster@example.net rf=arf ri=10 ro=e









































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Author's Address

   Scott Kitterman
   Authentication Metrics
   3611 Scheel Dr
   Ellicott City, MD  21042
   US

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









































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