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Levine 3 Internet-Draft Taughannock Networks 4 Updates: 6376 (if approved) 26 November 2019 5 Intended status: Informational 6 Expires: 29 May 2020 8 A Message Header to Identify Subscription Form Mail 9 draft-levine-mailbomb-header-02 11 Abstract 13 Many organizations have web forms that provoke an e-mail confirmation 14 to the e-mail address provided in the form. Malicious entities do 15 bulk form submissions with forged addresses, resulting in mail floods 16 to the holders of those addresses. This document defines a message 17 header to identify mail sent in response to web forms, so that 18 recipient mail systems can better recognize and mitigate the mail 19 floods. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on 29 May 2020. 38 Copyright Notice 40 Copyright (c) 2019 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 45 license-info) in effect on the date of publication of this document. 46 Please review these documents carefully, as they describe your rights 47 and restrictions with respect to this document. Code Components 48 extracted from this document must include Simplified BSD License text 49 as described in Section 4.e of the Trust Legal Provisions and are 50 provided without warranty as described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2 56 3. The Form-Sub header field . . . . . . . . . . . . . . . . . . 3 57 4. Mail flood enhanced status code . . . . . . . . . . . . . . . 4 58 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 59 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 60 6.1. Provisional Message Header Registry . . . . . . . . . . . 4 61 6.2. Enhanced Status Codes . . . . . . . . . . . . . . . . . . 5 62 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 63 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 64 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 6 65 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 67 1. Introduction 69 Discussion Venue: For the time being, discussion about this draft is 70 directed to the collaboration@mailman.m3aawg.org 71 (mailto:collaboration@mailman.m3aawg.org) mailing list. 73 Many organizations have web forms that provoke an e-mail confirmation 74 to the e-mail address provided in the form. Malicious entities 75 submit multiple forms with forged addresses, resulting in mail floods 76 to those addresses. We define a message header that identifies mail 77 sent in response to web forms, so that recipient mail systems can 78 better recognize and mitigate the mail floods. 80 Mail systems that recognize a mail flood may defer or reject the 81 mail. We also define an SMTP enhanced status code that a mail system 82 can use in a message rejection SMTP reponse to alert the sending 83 system that the message was rejected due to being part of a mail 84 flood. 86 2. Conventions 88 The terms Message Submission Agent (MSA) and Message Transfer Agent 89 (MTA) are defined as in [RFC5598]. 91 The ABNF [RFC5234] terms CRLF, FWS, and fields are imported from 92 [RFC5322]. 94 3. The Form-Sub header field 96 A MSA or an initial MTA adds a Form-Sub header field to indicate that 97 the message was sent in response to a web form submission. The 98 header consists of a semicolon-separated list of tag=value pairs. 99 The first tag-value pair is "v=1" to indicate that the header uses 100 the initial version of this specification. Receivers should ignore 101 Form-Sub headers with a v= tag that indicates an unknown version. 102 Subsequent tag-value pairs are optional, and receivers should ignore 103 pairs with unknown tags. 105 The tags ip4 or ip6 contain the IPv4 or IPv6 address, respectively, 106 from which the web form was submitted. The address may be partially 107 redacted for privacy reasons, by replacing groups of digits with the 108 letter "x", for example, 198.51.x.x or 2001:DB8::x or 109 x::1234:abcd:5678:ef01. If the sender cannot determine the 110 submitting IP address, it can include "ip=none". The goal of 111 including the IP address is to help receiving mail systems recognize 112 when a cluster of messages was provoked by the same submitter. Using 113 "x" rather than a hash of the the address provides a redaction that 114 cannot be reversed but still can be correlated among multiple 115 messages. 117 ABNF: 119 fields =/ "Form-Sub:" FWS "v=1" *(FWS ";" FWS fsarg) CRLF 121 fsarg = "ip4=" ip4redacted 122 ip4redacted = IPv4 address with parts optionally replaced by "x" 124 fsarg =/ "ip6=" ip6redacted 125 ip6redacted = IPv6 address with parts optionally replaced by "x" 127 fsarg =/ "ip=none" 129 fsarg =/ x-fsarg 131 x-fsarg =/ ALPHA *(ALPHA / DIGIT) "=" tagdata 132 tagdata = string of VCHAR excluding quote and semicolon 134 The Form-Sub header should be included within the set of the headers 135 signed by any DKIM [RFC6376] signature headers. 137 4. Mail flood enhanced status code 139 A mail receiver may choose to defer or reject mail that it recognizes 140 as part of a mail flood. It can include the enhanced status code 141 X.7.28 to indicate that the rejection is due to the message being 142 part of a mail flood that includes Form-Sub headers. 144 A sender would typically interpret the code as a strong hint that 145 their systems are being abused, so they should mitigate the abuse to 146 stop the mail flood. 148 5. Security Considerations 150 IP addresses are sometimes considered to be personally identifable 151 information. This specification allows partially redacted addresses 152 as a compromise to avoid identifying individual persons, while still 153 providing receivers a hint to recognize bulk submissions by the same 154 party. 156 The Form-Sub header discloses information from a sender to a 157 receiver, and the X.7.28 enhanced status code discloses information 158 from a receiver to a sender that they would not otherwise have. If 159 one party suspects the other is malicious, e.g., a receiver fears 160 that a sender is probing to see what its mail volume limits are, it 161 might not include the header or the status code for the possibly 162 malicious other party. 164 6. IANA Considerations 166 IANA has updated registries as follows. 168 6.1. Provisional Message Header Registry 170 The following value has been added to the Provisional Message Header 171 Registry 173 +-------------------+----------+----------+--------+-----------+ 174 | Header Field name | Template | Protocol | Status | Reference | 175 +===================+==========+==========+========+===========+ 176 | Form-Sub | . | mail | . | (this | 177 | | | | | document) | 178 +-------------------+----------+----------+--------+-----------+ 180 Table 1: Provisional Message Header Registry Added Value 182 6.2. Enhanced Status Codes 184 The following value has been added to the Enhanced Status Codes 185 Enumerated Status Codes Registry 187 +------+--------+----------+-----------+---------+---------+-------------------+ 188 | Code | Sample |Associated|Description|Reference|Submitter| Change Controller | 189 | | Text | Basic | | | | | 190 | | | Status | | | | | 191 | | | Code | | | | | 192 +======+========+==========+===========+=========+=========+===================+ 193 |X.7.28| Mail | . |The message| [this | J. |standards@taugh.com| 194 | | flood | |appears to |document]| Levine | | 195 | |detected| |be part of | | | | 196 | | | | a mail | | | | 197 | | | | flood of | | | | 198 | | | | similar | | | | 199 | | | | abusive | | | | 200 | | | | messages. | | | | 201 +------+--------+----------+-----------+---------+---------+-------------------+ 203 Table 2: Enumerated Status Codes Registry Added Value 205 7. Acknowledgments 207 Kurt Andersen and the M3AAWG Collaboration Committee provided the 208 good parts. 210 8. Normative References 212 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 213 Specifications: ABNF", STD 68, RFC 5234, 214 DOI 10.17487/RFC5234, January 2008, 215 . 217 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, 218 DOI 10.17487/RFC5322, October 2008, 219 . 221 [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, 222 DOI 10.17487/RFC5598, July 2009, 223 . 225 [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., 226 "DomainKeys Identified Mail (DKIM) Signatures", STD 76, 227 RFC 6376, DOI 10.17487/RFC6376, September 2011, 228 . 230 Appendix A. Change log 232 01 to 02 Convert to v3 xml 234 00 to 01 Fix ABNF to allow arbitrary tags. Fix typos. 236 Author's Address 238 John Levine 239 Taughannock Networks 240 PO Box 727 241 Trumansburg 243 Email: standards@taugh.com