TCP Maintenance and Minor Extensions F. Gont (tcpm) UTN-FRH / SI6 Networks Internet-Draft March 29, 2012 Updates: 793 (if approved) Intended status: Standards Track Expires: September 30, 2012 Processing of TCP segments with Mirrored End-points draft-gont-tcpm-tcp-mirrored-endpoints-00.txt Abstract This document describes a problem found in some popular implementations regarding the processing of TCP segments in which the local endpoint is equal to the remote endpoint. Additionally, it formally updates RFC 793 clarifying how this scenario should be handled. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 30, 2012. 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 Gont Expires September 30, 2012 [Page 1] Internet-Draft TCP segments with mirrored endpoints March 2012 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Updating RFC 793 . . . . . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 3 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6.1. Normative References . . . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 4 Gont Expires September 30, 2012 [Page 2] Internet-Draft TCP segments with mirrored endpoints March 2012 1. Introduction Some systems have been found to be unable to process TCP segments in which the source endpoint {Source Address, Source Port} is the same than the destination end-point {Destination Address, Destination Port}. Such TCP segments have been reported to cause malfunction of a number of implementations [CERT1996], and have been exploited in the past to perform Denial of Service (DoS) attacks [Meltman1997]. While these packets are very very unlikely to exist in legitimate scenarios, TCP should nevertheless be able to process them without the need of any "extra" code. 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 RFC 2119 [RFC2119]. 2. Updating RFC 793 TCP MUST be able to gracefully handle the case where the source end- point (IP Source Address, TCP Source Port) is the same as the destination end-point (IP Destination Address, TCP Destination Port). A SYN segment in which the source end-point {Source Address, Source Port} is the same as the destination end-point {Destination Address, Destination Port} will result in a "simultaneous open" scenario, such as the one described in page 32 of RFC 793 [RFC0793]. Therefore, those TCP implementations that correctly handle simultaneous opens should already be prepared to handle these unusual TCP segments. 3. IANA Considerations This document has no IANA actions. The RFC Editor is requested to remove this section before publishing this document as an RFC. 4. Security Considerations This document describes a problem found in some popular implementations regarding the processing of TCP instances in which the local and the remote TCP endpoints are the equal. It formally updates RFC 793, clarifying how such packets should be handled, thus helping prevent unexpected behaviors in host implementations. Gont Expires September 30, 2012 [Page 3] Internet-Draft TCP segments with mirrored endpoints March 2012 5. Acknowledgements The author would like to thank David Borman for a fruitful discussion about this topic at IETF 73 (Minneapolis). This document is based on the technical report "Security Assessment of the Transmission Control Protocol (TCP)" [CPNI-TCP] written by Fernando Gont on behalf of the UK CPNI. Fernando Gont would like to thank the UK CPNI for their continued support. 6. References 6.1. Normative References [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 6.2. Informative References [CERT1996] CERT, "CERT Advisory CA-1996-21: TCP SYN Flooding and IP Spoofing Attacks", 1996, . [CPNI-TCP] Gont, F., "CPNI Technical Note 3/2009: Security Assessment of the Transmission Control Protocol (TCP)", 2009, . [Meltman1997] Meltman, "new TCP/IP bug in win95. Post to the bugtraq mailing-list", 1996, . Gont Expires September 30, 2012 [Page 4] Internet-Draft TCP segments with mirrored endpoints March 2012 Author's Address Fernando Gont UTN-FRH / SI6 Networks Evaristo Carriego 2644 Haedo, Provincia de Buenos Aires 1706 Argentina Phone: +54 11 4650 8472 Email: fgont@si6networks.com URI: http://www.si6networks.com Gont Expires September 30, 2012 [Page 5]