Improving TCP's Robustness to Blind In-Window Attacks
RFC 5961
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(August 2010; Errata)
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RFC 5961 (Proposed Standard)
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Internet Engineering Task Force (IETF) A. Ramaiah
Request for Comments: 5961 Cisco
Category: Standards Track R. Stewart
ISSN: 2070-1721 Huawei
M. Dalal
Cisco
August 2010
Improving TCP's Robustness to Blind In-Window Attacks
Abstract
TCP has historically been considered to be protected against spoofed
off-path packet injection attacks by relying on the fact that it is
difficult to guess the 4-tuple (the source and destination IP
addresses and the source and destination ports) in combination with
the 32-bit sequence number(s). A combination of increasing window
sizes and applications using longer-term connections (e.g., H-323 or
Border Gateway Protocol (BGP) [RFC4271]) have left modern TCP
implementations more vulnerable to these types of spoofed packet
injection attacks.
Many of these long-term TCP applications tend to have predictable IP
addresses and ports that makes it far easier for the 4-tuple (4-tuple
is the same as the socket pair mentioned in RFC 793) to be guessed.
Having guessed the 4-tuple correctly, an attacker can inject a TCP
segment with the RST bit set, the SYN bit set or data into a TCP
connection by systematically guessing the sequence number of the
spoofed segment to be in the current receive window. This can cause
the connection to abort or cause data corruption. This document
specifies small modifications to the way TCP handles inbound segments
that can reduce the chances of a successful attack.
Status of This Memo
This is an Internet Standards Track document.
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). Further information on
Internet Standards is available in 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/rfc5961.
Ramaiah, et al. Standards Track [Page 1]
RFC 5961 TCP Security August 2010
Copyright Notice
Copyright (c) 2010 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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
1.1. Applicability Statement ....................................3
1.2. Basic Attack Methodology ...................................4
1.3. Attack probabilities .......................................5
2. Terminology .....................................................7
3. Blind Reset Attack Using the RST Bit ............................7
3.1. Description of the Attack ..................................7
3.2. Mitigation .................................................7
4. Blind Reset Attack Using the SYN Bit ............................9
4.1. Description of the Attack ..................................9
4.2. Mitigation .................................................9
5. Blind Data Injection Attack ....................................10
5.1. Description of the Attack .................................10
5.2. Mitigation ................................................11
6. Suggested Mitigation Strengths .................................12
7. ACK Throttling .................................................12
8. Backward Compatibility and Other Considerations ................13
9. Middlebox Considerations .......................................14
9.1. Middlebox That Resend RSTs ................................14
9.2. Middleboxes That Advance Sequence Numbers .................15
9.3. Middleboxes That Drop the Challenge ACK ...................15
10. Security Considerations .......................................16
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