Internet DRAFT - draft-levine-mailbomb-header
draft-levine-mailbomb-header
Network Working Group J.R. Levine
Internet-Draft Taughannock Networks
Updates: 6376 (if approved) 26 November 2019
Intended status: Informational
Expires: 29 May 2020
A Message Header to Identify Subscription Form Mail
draft-levine-mailbomb-header-02
Abstract
Many organizations have web forms that provoke an e-mail confirmation
to the e-mail address provided in the form. Malicious entities do
bulk form submissions with forged addresses, resulting in mail floods
to the holders of those addresses. This document defines a message
header to identify mail sent in response to web forms, so that
recipient mail systems can better recognize and mitigate the mail
floods.
Status of This Memo
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This Internet-Draft will expire on 29 May 2020.
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Please review these documents carefully, as they describe your rights
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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. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The Form-Sub header field . . . . . . . . . . . . . . . . . . 3
4. Mail flood enhanced status code . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6.1. Provisional Message Header Registry . . . . . . . . . . . 4
6.2. Enhanced Status Codes . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Discussion Venue: For the time being, discussion about this draft is
directed to the collaboration@mailman.m3aawg.org
(mailto:collaboration@mailman.m3aawg.org) mailing list.
Many organizations have web forms that provoke an e-mail confirmation
to the e-mail address provided in the form. Malicious entities
submit multiple forms with forged addresses, resulting in mail floods
to those addresses. We define a message header that identifies mail
sent in response to web forms, so that recipient mail systems can
better recognize and mitigate the mail floods.
Mail systems that recognize a mail flood may defer or reject the
mail. We also define an SMTP enhanced status code that a mail system
can use in a message rejection SMTP reponse to alert the sending
system that the message was rejected due to being part of a mail
flood.
2. Conventions
The terms Message Submission Agent (MSA) and Message Transfer Agent
(MTA) are defined as in [RFC5598].
The ABNF [RFC5234] terms CRLF, FWS, and fields are imported from
[RFC5322].
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3. The Form-Sub header field
A MSA or an initial MTA adds a Form-Sub header field to indicate that
the message was sent in response to a web form submission. The
header consists of a semicolon-separated list of tag=value pairs.
The first tag-value pair is "v=1" to indicate that the header uses
the initial version of this specification. Receivers should ignore
Form-Sub headers with a v= tag that indicates an unknown version.
Subsequent tag-value pairs are optional, and receivers should ignore
pairs with unknown tags.
The tags ip4 or ip6 contain the IPv4 or IPv6 address, respectively,
from which the web form was submitted. The address may be partially
redacted for privacy reasons, by replacing groups of digits with the
letter "x", for example, 198.51.x.x or 2001:DB8::x or
x::1234:abcd:5678:ef01. If the sender cannot determine the
submitting IP address, it can include "ip=none". The goal of
including the IP address is to help receiving mail systems recognize
when a cluster of messages was provoked by the same submitter. Using
"x" rather than a hash of the the address provides a redaction that
cannot be reversed but still can be correlated among multiple
messages.
ABNF:
fields =/ "Form-Sub:" FWS "v=1" *(FWS ";" FWS fsarg) CRLF
fsarg = "ip4=" ip4redacted
ip4redacted = IPv4 address with parts optionally replaced by "x"
fsarg =/ "ip6=" ip6redacted
ip6redacted = IPv6 address with parts optionally replaced by "x"
fsarg =/ "ip=none"
fsarg =/ x-fsarg
x-fsarg =/ ALPHA *(ALPHA / DIGIT) "=" tagdata
tagdata = string of VCHAR excluding quote and semicolon
The Form-Sub header should be included within the set of the headers
signed by any DKIM [RFC6376] signature headers.
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4. Mail flood enhanced status code
A mail receiver may choose to defer or reject mail that it recognizes
as part of a mail flood. It can include the enhanced status code
X.7.28 to indicate that the rejection is due to the message being
part of a mail flood that includes Form-Sub headers.
A sender would typically interpret the code as a strong hint that
their systems are being abused, so they should mitigate the abuse to
stop the mail flood.
5. Security Considerations
IP addresses are sometimes considered to be personally identifable
information. This specification allows partially redacted addresses
as a compromise to avoid identifying individual persons, while still
providing receivers a hint to recognize bulk submissions by the same
party.
The Form-Sub header discloses information from a sender to a
receiver, and the X.7.28 enhanced status code discloses information
from a receiver to a sender that they would not otherwise have. If
one party suspects the other is malicious, e.g., a receiver fears
that a sender is probing to see what its mail volume limits are, it
might not include the header or the status code for the possibly
malicious other party.
6. IANA Considerations
IANA has updated registries as follows.
6.1. Provisional Message Header Registry
The following value has been added to the Provisional Message Header
Registry
+-------------------+----------+----------+--------+-----------+
| Header Field name | Template | Protocol | Status | Reference |
+===================+==========+==========+========+===========+
| Form-Sub | . | mail | . | (this |
| | | | | document) |
+-------------------+----------+----------+--------+-----------+
Table 1: Provisional Message Header Registry Added Value
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6.2. Enhanced Status Codes
The following value has been added to the Enhanced Status Codes
Enumerated Status Codes Registry
+------+--------+----------+-----------+---------+---------+-------------------+
| Code | Sample |Associated|Description|Reference|Submitter| Change Controller |
| | Text | Basic | | | | |
| | | Status | | | | |
| | | Code | | | | |
+======+========+==========+===========+=========+=========+===================+
|X.7.28| Mail | . |The message| [this | J. |standards@taugh.com|
| | flood | |appears to |document]| Levine | |
| |detected| |be part of | | | |
| | | | a mail | | | |
| | | | flood of | | | |
| | | | similar | | | |
| | | | abusive | | | |
| | | | messages. | | | |
+------+--------+----------+-----------+---------+---------+-------------------+
Table 2: Enumerated Status Codes Registry Added Value
7. Acknowledgments
Kurt Andersen and the M3AAWG Collaboration Committee provided the
good parts.
8. Normative References
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
DOI 10.17487/RFC5598, July 2009,
<https://www.rfc-editor.org/info/rfc5598>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011,
<https://www.rfc-editor.org/info/rfc6376>.
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Appendix A. Change log
01 to 02 Convert to v3 xml
00 to 01 Fix ABNF to allow arbitrary tags. Fix typos.
Author's Address
John Levine
Taughannock Networks
PO Box 727
Trumansburg
Email: standards@taugh.com
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