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Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Looks like a reference, but probably isn't: '1' on line 241 Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Levine 3 Internet-Draft Taughannock Networks 4 Updates: 6376 (if approved) October 5, 2017 5 Intended status: Informational 6 Expires: April 8, 2018 8 A Message Header to Identify Subscription Form Mail 9 draft-levine-mailbomb-header-01 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 April 8, 2018. 38 Copyright Notice 40 Copyright (c) 2017 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 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2 57 3. The Form-Sub header field . . . . . . . . . . . . . . . . . . 3 58 4. Mail flood enhanced status code . . . . . . . . . . . . . . . 3 59 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 60 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 61 6.1. Provisional Message Header Registry . . . . . . . . . . . 4 62 6.2. Enhanced Status Codes . . . . . . . . . . . . . . . . . . 4 63 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 64 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 66 8.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 6 68 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 70 1. Introduction 72 Discussion Venue: For the time being, discussion about this draft 73 is directed to the collaboration@mailman.m3aawg.org [1] mailing 74 list. 76 Many organizations have web forms that provoke an e-mail confirmation 77 to the e-mail address provided in the form. Malicious entities 78 submit multiple forms with forged addresses, resulting in mail floods 79 to those addresses. We define a message header that identifies mail 80 sent in response to web forms, so that recipient mail systems can 81 better recognize and mitigate the mail floods. 83 Mail systems that recognize a mail flood may defer or reject the 84 mail. We also define an SMTP enhanced status code that a mail system 85 can use in a message rejection SMTP reponse to alert the sending 86 system that the message was rejected due to being part of a mail 87 flood. 89 2. Conventions 91 The terms Message Submission Agent (MSA) and Message Transfer Agent 92 (MTA) are defined as in [RFC5598]. 94 The ABNF [RFC5234] terms CRLF, FWS, and fields are imported from 95 [RFC5322]. 97 3. The Form-Sub header field 99 A MSA or an initial MTA adds a Form-Sub header field to indicate that 100 the message was sent in response to a web form submission. The 101 header consists of a semicolon-separated list of tag=value pairs. 102 The first tag-value pair is "v=1" to indicate that the header uses 103 the initial version of this specification. Receivers should ignore 104 Form-Sub headers with a v= tag that indicates an unknown version. 105 Subsequent tag-value pairs are optional, and receivers should ignore 106 pairs with unknown tags. 108 The tags ip4 or ip6 contain the IPv4 or IPv6 address, respectively, 109 from which the web form was submitted. The address may be partially 110 redacted for privacy reasons, by replacing groups of digits with the 111 letter "x", for example, 198.51.x.x or 2001:DB8::x or 112 x::1234:abcd:5678:ef01. If the sender cannot determine the 113 submitting IP address, it can include "ip=none". The goal of 114 including the IP address is to help receiving mail systems recognize 115 when a cluster of messages was provoked by the same submitter. Using 116 "x" rather than a hash of the the address provides a redaction that 117 cannot be reversed but still can be correlated among multiple 118 messages. 120 ABNF: 122 fields =/ "Form-Sub:" FWS "v=1" *(FWS ";" FWS fsarg) CRLF 124 fsarg = "ip4=" ip4redacted 125 ip4redacted = IPv4 address with parts optionally replaced by "x" 127 fsarg =/ "ip6=" ip6redacted 128 ip6redacted = IPv6 address with parts optionally replaced by "x" 130 fsarg =/ "ip=none" 132 fsarg =/ x-fsarg 134 x-fsarg =/ ALPHA *(ALPHA / DIGIT) "=" tagdata 135 tagdata = string of VCHAR excluding quote and semicolon 137 The Form-Sub header should be included within the set of the headers 138 signed by any DKIM [RFC6376] signature headers. 140 4. Mail flood enhanced status code 142 A mail receiver may choose to defer or reject mail that it recognizes 143 as part of a mail flood. It can include the enhanced status code 144 X.7.28 to indicate that the rejection is due to the message being 145 part of a mail flood that includes Form-Sub headers. 147 A sender would typically interpret the code as a strong hint that 148 their systems are being abused, so they should mitigate the abuse to 149 stop the mail flood. 151 5. Security Considerations 153 IP addresses are sometimes considered to be personally identifable 154 information. This specification allows partially redacted addresses 155 as a compromise to avoid identifying individual persons, while still 156 providing receivers a hint to recognize bulk submissions by the same 157 party. 159 The Form-Sub header discloses information from a sender to a 160 receiver, and the X.7.28 enhanced status code discloses information 161 from a receiver to a sender that they would not otherwise have. If 162 one party suspects the other is malicious, e.g., a receiver fears 163 that a sender is probing to see what its mail volume limits are, it 164 might not include the header or the status code for the possibly 165 malicious other party. 167 6. IANA Considerations 169 IANA has updated registries as follows. 171 6.1. Provisional Message Header Registry 173 The following value has been added to the Provisional Message Header 174 Registry 176 +------------------+----------+----------+--------+-----------------+ 177 | Header Field | Template | Protocol | Status | Reference | 178 | name | | | | | 179 +------------------+----------+----------+--------+-----------------+ 180 | Form-Sub | . | mail | . | (this document) | 181 +------------------+----------+----------+--------+-----------------+ 183 Table 1: Provisional Message Header Registry Added Value 185 6.2. Enhanced Status Codes 187 The following value has been added to the Enhanced Status Codes 188 Enumerated Status Codes Registry 189 +------+-------+--------+---------+--------+--------+---------------+ 190 | Code | Sampl | Associ | Descrip | Refere | Submit | Change | 191 | | e | ated | tion | nce | ter | Controller | 192 | | Text | Basic | | | | | 193 | | | Status | | | | | 194 | | | Code | | | | | 195 +------+-------+--------+---------+--------+--------+---------------+ 196 | X.7. | Mail | . | The | [this | J. | standards@tau | 197 | 28 | flood | | message | docume | Levine | gh.com | 198 | | detec | | appears | nt] | | | 199 | | ted | | to be | | | | 200 | | | | part of | | | | 201 | | | | a mail | | | | 202 | | | | flood | | | | 203 | | | | of | | | | 204 | | | | similar | | | | 205 | | | | abusive | | | | 206 | | | | message | | | | 207 | | | | s. | | | | 208 +------+-------+--------+---------+--------+--------+---------------+ 210 Table 2: Enunerated Status Codes Registry Added Value 212 7. Acknowledgments 214 Kurt Andersen and the M3AAWG Collaboration Committee provided the 215 good parts. 217 8. References 219 8.1. Normative References 221 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 222 Specifications: ABNF", STD 68, RFC 5234, 223 DOI 10.17487/RFC5234, January 2008, 224 . 226 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, 227 DOI 10.17487/RFC5322, October 2008, 228 . 230 [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, 231 DOI 10.17487/RFC5598, July 2009, 232 . 234 [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., 235 "DomainKeys Identified Mail (DKIM) Signatures", STD 76, 236 RFC 6376, DOI 10.17487/RFC6376, September 2011, 237 . 239 8.2. URIs 241 [1] mailto:collaboration@mailman.m3aawg.org 243 Appendix A. Change log 245 00 to 01: Fix ABNF to allow arbitrary tags. Fix typos. . 247 Author's Address 249 John Levine 250 Taughannock Networks 251 PO Box 727 252 Trumansburg, NY 14886 254 Phone: +883.5100.01196712 255 Email: standards@taugh.com