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Updates:
Keywords: [--------], fraud, phishing, spoofing
Internet Engineering Task Force (IETF) S. Kitterman
Request for Comments: 6652 Agari
Updates: 4408 June 2012
Category: Standards Track
ISSN: 2070-1721
Sender Policy Framework (SPF) Authentication Failure Reporting
Using the Abuse Reporting Format
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.
This memo updates RFC 4408 by providing an IANA registry for SPF
modifiers.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6652.
Copyright Notice
Copyright (c) 2012 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
(http://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.
Kitterman Standards Track [Page 1]
RFC 6652 SPF Auth Failure Reporting June 2012
Table of Contents
1. Introduction ....................................................2
2. Definitions .....................................................3
2.1. Key Words ..................................................3
2.2. Imported Definitions .......................................3
3. Optional Reporting Address for SPF ..............................3
4. Requested Reports ...............................................4
4.1. Requested Reports for SPF Failures .........................5
5. IANA Considerations .............................................5
5.1. SPF Modifier Registration ..................................5
6. Security Considerations .........................................6
6.1. Identity Selection .........................................6
6.2. Report Volume ..............................................6
7. References ......................................................7
7.1. Normative References .......................................7
7.2. Informative References .....................................7
Appendix A. Acknowledgements .......................................8
Appendix B. Examples ...............................................8
B.1. SPF DNS Record for Domain That Sends No Mail but
Requests Reports ...........................................8
B.2. Minimal SPF DNS Record Change to Add a Reporting
Address ....................................................8
B.3. SPF DNS Record with Reporting Address, Report
Percentage, and Requested Report Type ......................8
1. Introduction
The Abuse Reporting Format [ARF] defines a message format for sending
reports of abuse in the messaging infrastructure, with an eye toward
automating both the generation and consumption of those reports.
The Sender Policy Framework [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. 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.).
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 [ARF-AUTHFAIL] and
[ARF-AS].
This document additionally creates a an IANA registry of [SPF] record
modifiers to avoid modifier namespace collisions.
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RFC 6652 SPF Auth Failure Reporting June 2012
2. Definitions
2.1. Key Words
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].
3. Optional Reporting Address for SPF
There exist cases in which an ADministrative Management Domain (ADMD)
(see [EMAIL-ARCH]) 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-compliant domain per Section 4.1 of [SPF]. ra= modifiers in
a record that was reached by following an "include" mechanism
(defined in Section 5.2 of [SPF]) MUST be ignored.
ABNF:
spf-report-tag = "ra=" qp-section
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RFC 6652 SPF Auth Failure Reporting June 2012
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 SPF 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. An exception to this might be some
out-of-band arrangement between two parties to override it with
some mutually agreed value. 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 = "rp=" 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.
ABNF:
spf-rr-type = ( "all" / "e" / "f" / "s" / "n" )
spf-rr-tag = "rr=" spf-rr-type *( ":" 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.
4. Requested Reports
This memo also includes, as the "rr" 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 list.
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RFC 6652 SPF Auth Failure Reporting June 2012
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".
5. IANA Considerations
As required by [IANA-CONS], this section contains registry
information for the new [SPF] modifiers.
5.1. SPF Modifier Registration
IANA has created the Modifier Names registry under Sender Policy
Framework Parameters, to include a list of all registered SPF
modifier names and their defining documents.
New registrations or updates are to be published in accordance with
the "Specification Required" guidelines as described in [IANA-CONS].
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 the following:
Current: The field is in current use
Deprecated: The field might be in current use but its use is
discouraged
Historic: The field is no longer in current use
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RFC 6652 SPF Auth Failure Reporting June 2012
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 | RFC 4408 | Current |
| redirect | RFC 4408 | Current |
| ra | (this document) | Current |
| rp | (this document) | Current |
| rr | (this document) | Current |
+------------+-----------------+---------+
6. Security Considerations
Inherited considerations: implementers are advised to consider the
Security Considerations sections of [SPF], [ARF], [ARF-AS], and
[ARF-AUTHFAIL].
In addition to the advice in the Security Considerations section of
[ARF-AS], these additional considerations apply to the generation of
[SPF] authentication failure reports:
6.1. Identity Selection
Preventing an [SPF] failure for SPF authentication failure reports is
essential to mitigate the risk of data loops.
If the [SMTP] return address to be used will not be the NULL
return address, i.e., "MAIL FROM:<>", then the selected return
address MUST be selected such that it will pass [SPF] MAIL FROM
checks upon initial receipt.
If the report is passed to the Message Submission Agent (MSA) (MSA
is described in [EMAIL-ARCH] using [SMTP]), the HELO/EHLO command
parameter SHOULD also be selected so that it will pass [SPF] HELO
checks.
6.2. Report Volume
It is impossible to predict the volume of reports this facility will
generate when enabled by a report receiver. An implementer ought to
anticipate substantial volume, since the amount of abuse occurring at
receivers cannot be known ahead of time, and may vary rapidly and
unpredictably.
Kitterman Standards Track [Page 6]
RFC 6652 SPF Auth Failure Reporting June 2012
7. References
7.1. Normative References
[ABNF] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008.
[ARF] Shafranovich, Y., Levine, J., and M. Kucherawy, "An
Extensible Format for Email Feedback Reports", RFC 5965,
August 2010.
[ARF-AS] Falk, J. and M. Kucherawy, Ed., "Creation and Use of Email
Feedback Reports: An Applicability Statement for the Abuse
Reporting Format (ARF)", RFC 6650, June 2012.
[ARF-AUTHFAIL]
Fontana, H., "Authentication Failure Reporting Using the
Abuse Reporting Format", RFC 6591, April 2012.
[IANA-CONS]
Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[MAIL] Resnick, P., Ed., "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
[EMAIL-ARCH]
Crocker, D., "Internet Mail Architecture", RFC 5598,
July 2009.
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RFC 6652 SPF Auth Failure Reporting June 2012
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.
Appendix B. Examples
B.1. SPF DNS Record for Domain That Sends No Mail but Requests Reports
v=spf1 ra=postmaster -all
B.2. Minimal SPF DNS Record Change to Add a Reporting Address
v=spf1 mx:example.org ra=postmaster -all
B.3. SPF DNS Record with Reporting Address, Report Percentage, and
Requested Report Type
v=spf1 mx:example.org -all ra=postmaster rp=10 rr=e
Author's Address
Scott Kitterman
Agari
3611 Scheel Dr.
Ellicott City, MD 21042
US
Phone: +1 301 325 5475
EMail: scott@kitterman.com
Kitterman Standards Track [Page 8]