ARF Source Port: Source Ports in Abuse Reporting Format (ARF) Reports
A new ARF header field that names the source port, so an abuse report can pinpoint who sent the mail.
Clayton, R. and M. Kucherawy, "Source Ports in Abuse Reporting Format (ARF) Reports", RFC 6692, DOI 10.17487/RFC6692, July 2012, <https://www.rfc-editor.org/info/rfc6692>.
@misc{rfc6692,
series = {Request for Comments},
number = 6692,
howpublished = {RFC 6692},
publisher = {RFC Editor},
doi = {10.17487/RFC6692},
url = {https://www.rfc-editor.org/info/rfc6692},
author = {R. Clayton and M. Kucherawy},
title = {{Source Ports in Abuse Reporting Format (ARF) Reports}},
pagetotal = 5,
year = 2012,
month = jul,
} RFC text
Contents
Internet Engineering Task Force (IETF) R. Clayton
Request for Comments: 6692 University of Cambridge
Updates: 6591 M. Kucherawy
Category: Standards Track Cloudmark, Inc.
ISSN: 2070-1721 July 2012
Source Ports in Abuse Reporting Format (ARF) Reports
Abstract
This document defines an additional header field for use in Abuse
Reporting Format (ARF) reports to permit the identification of the
source port of the connection involved in an abuse incident.
This document updates RFC 6591.
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/rfc6692.
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.
Table of Contents
1. Introduction ....................................................2
2. Keywords ........................................................2
3. Source-Port Field Definition ....................................2
4. Time Accuracy ...................................................3
5. IANA Considerations .............................................3
6. Security Considerations .........................................3
7. References ......................................................4
7.1. Normative References .......................................4
7.2. Informative References .....................................4
Appendix A. Acknowledgements .......................................5
1. Introduction
[ARF] defined the Abuse Reporting Format, an extensible message
format for Email Feedback Reports. These reports are used to report
incidents of email abuse. ARF was extended by [AUTHFAILURE-REPORT]
to enable the reporting of email authentication failures. These
specifications provided for the source IP address to be included in a
report. As explained in [LOG], the deployment of IP address sharing
techniques requires the source port values to be included in reports
if unambiguous identification of the origin of abuse is to be
achieved.
This document defines an ARF reporting field to contain this
information and provides guidance for its use.
2. 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].
3. Source-Port Field Definition
A new ARF header field called "Source-Port" is defined. When present
in a report, it MUST contain the client port of the TCP connection
from which the reported message originated, corresponding to the
"Source-IP" field that contains the client address of that same
connection, thereby describing completely the origin of the abuse
incident.
Per, [ABNF], the formal syntax is:
source-port = "Source-Port:" [CFWS] 1*5DIGIT [CFWS] CRLF
"CFWS", which represents email-style comments or folding white space,
is imported from [MAIL].
When any report is generated that includes the "Source-IP" field (see
Section 3.2 of [ARF]), this field SHOULD also be present, unless the
port number is unavailable.
Use of this field is RECOMMENDED for reports generated per
[AUTHFAILURE-REPORT] (see Section 3.1 of that document).
4. Time Accuracy
[LOG] underscores the importance of accurate clocks when generating
reports that include source port information because of the fact that
source ports can be recycled very quickly in Internet Service
Provider environments. The same considerations described there apply
here.
Report generators that include an Arrival-Date report field MAY
choose to express the value of that date in Universal Coordinated
Time (UTC) to enable simpler correlation with local records at sites
that are following the provisions of [LOG].
5. IANA Considerations
IANA has added the following entry to the "Feedback Report Header
Fields" registry:
Field Name: Source-Port
Description: TCP source port from which the original message was
received
Multiple Appearances: No
Related "Feedback-Type": any
Reference: [RFC6692]
Status: current
6. Security Considerations
This extension introduces no new security considerations not already
covered in [ARF].
Some security considerations related to the general topic of source
port logging can be found in [LOG].
7. References
7.1. Normative References
[ABNF] Crocker, D. 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.
[AUTHFAILURE-REPORT]
Fontana, H., "Authentication Failure Reporting Using the
Abuse Reporting Format", RFC 6591, April 2012.
[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.
7.2. Informative References
[LOG] Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
"Logging Recommendations for Internet-Facing Servers",
BCP 162, RFC 6302, June 2011.
Appendix A. Acknowledgements
The authors wish to acknowledge the following for their review and
constructive criticism of this proposal: Steve Atkins, Scott
Kitterman, John Levine, and Doug Otis.
The idea for this work originated within the Messaging Anti-Abuse
Working Group (MAAWG).
Authors' Addresses
Richard Clayton
University of Cambridge
Computer Laboratory
JJ Thomson Avenue
Cambridge CB3 0FD
United Kingdom
Phone: +44 1223 763570
EMail: richard.clayton@cl.cam.ac.uk
Murray S. Kucherawy
Cloudmark, Inc.
128 King St., 2nd Floor
San Francisco, CA 94107
US
Phone: +1 415 946 3800
EMail: superuser@gmail.com
AI ELI5
On this page
§1Why a Source Port Is Needed
The Abuse Reporting Format (ARF) is an extensible message format for email feedback reports, which report incidents of email abuse. RFC 6591 extended it to report email authentication failures. Both let a report include the source IP address.
The RFC explains, citing another document, that IP address sharing techniques are now deployed. When many clients share an address, the source port values must be in the report if the origin of the abuse is to be identified unambiguously.
If lots of kids share one house address, a letter to that address does not say which kid did it. The door number inside the house tells you.
§3The Source-Port Field
A new ARF header field called Source-Port is defined. When present, it MUST contain the client port of the TCP connection from which the reported message originated. This is the same connection whose client address is in the Source-IP field.
Generators SHOULD include the field in any report that has a Source-IP field, unless the port number is unavailable. Its use is RECOMMENDED for authentication failure reports generated under RFC 6591.
The formal syntax allows optional comments or folding white space around one to five digits.
The new line in the complaint says which door number the message came from, matching the street address already written there.
§4Clock Accuracy and IANA
Source ports can be recycled very quickly in Internet Service Provider environments, so accurate clocks matter when reports include port information. A report generator that includes an Arrival-Date field MAY express it in UTC to make it easier to match against local records.
IANA added Source-Port to the "Feedback Report Header Fields" registry. It may appear only once per report and can be related to any Feedback-Type.
Door numbers get handed to new visitors fast, so you need to know exactly what time the message came. Then you can match it to the right visitor.
§6Security Considerations
The extension introduces no new security considerations beyond those already covered in the base ARF specification. Some considerations about logging source ports in general can be found in the logging recommendations document the RFC cites.
Adding a door number does not open any new doors for bad guys.