ICMP Attacks against TCP
RFC 5927

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Internet Engineering Task Force (IETF)                           F. Gont
Request for Comments: 5927                                       UTN/FRH
Category: Informational                                        July 2010
ISSN: 2070-1721

                        ICMP Attacks against TCP

Abstract

   This document discusses the use of the Internet Control Message
   Protocol (ICMP) to perform a variety of attacks against the
   Transmission Control Protocol (TCP).  Additionally, this document
   describes a number of widely implemented modifications to TCP's
   handling of ICMP error messages that help to mitigate these issues.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc5927.

Gont                          Informational                     [Page 1]
RFC 5927                ICMP Attacks against TCP               July 2010

Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
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   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Gont                          Informational                     [Page 2]
RFC 5927                ICMP Attacks against TCP               July 2010

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  The Internet Control Message Protocol (ICMP) . . . . . . .  5
       2.1.1.  ICMP for IP version 4 (ICMPv4) . . . . . . . . . . . .  5
       2.1.2.  ICMP for IP version 6 (ICMPv6) . . . . . . . . . . . .  6
     2.2.  Handling of ICMP Error Messages  . . . . . . . . . . . . .  6
     2.3.  Handling of ICMP Error Messages in the Context of IPsec  .  7
   3.  Constraints in the Possible Solutions  . . . . . . . . . . . .  8
   4.  General Counter-Measures against ICMP Attacks  . . . . . . . . 10
     4.1.  TCP Sequence Number Checking . . . . . . . . . . . . . . . 10
     4.2.  Port Randomization . . . . . . . . . . . . . . . . . . . . 11
     4.3.  Filtering ICMP Error Messages Based on the ICMP Payload  . 11
   5.  Blind Connection-Reset Attack  . . . . . . . . . . . . . . . . 12
     5.1.  Description  . . . . . . . . . . . . . . . . . . . . . . . 12
     5.2.  Attack-Specific Counter-Measures . . . . . . . . . . . . . 13
   6.  Blind Throughput-Reduction Attack  . . . . . . . . . . . . . . 16
     6.1.  Description  . . . . . . . . . . . . . . . . . . . . . . . 16
     6.2.  Attack-Specific Counter-Measures . . . . . . . . . . . . . 16
   7.  Blind Performance-Degrading Attack . . . . . . . . . . . . . . 16
     7.1.  Description  . . . . . . . . . . . . . . . . . . . . . . . 16
     7.2.  Attack-Specific Counter-Measures . . . . . . . . . . . . . 18
     7.3.  The Counter-Measure for the PMTUD Attack in Action . . . . 22
       7.3.1.  Normal Operation for Bulk Transfers  . . . . . . . . . 22
       7.3.2.  Operation during Path-MTU Changes  . . . . . . . . . . 24
       7.3.3.  Idle Connection Being Attacked . . . . . . . . . . . . 25
       7.3.4.  Active Connection Being Attacked after Discovery
               of the Path-MTU  . . . . . . . . . . . . . . . . . . . 26