Security Implications of Predictable Fragment Identification Values
RFC 7739
Document | Type | RFC - Informational (February 2016; No errata) | |
---|---|---|---|
Author | Fernando Gont | ||
Last updated | 2016-02-02 | ||
Replaces | draft-gont-6man-predictable-fragment-id | ||
Stream | Internent Engineering Task Force (IETF) | ||
Formats | plain text html pdf htmlized (tools) htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Bob Hinden | ||
Shepherd write-up | Show (last changed 2015-06-09) | ||
IESG | IESG state | RFC 7739 (Informational) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Yes | ||
Telechat date | |||
Responsible AD | Brian Haberman | ||
Send notices to | (None) | ||
IANA | IANA review state | IANA OK - No Actions Needed | |
IANA action state | No IANA Actions |
Internet Engineering Task Force (IETF) F. Gont Request for Comments: 7739 Huawei Technologies Category: Informational February 2016 ISSN: 2070-1721 Security Implications of Predictable Fragment Identification Values Abstract IPv6 specifies the Fragment Header, which is employed for the fragmentation and reassembly mechanisms. The Fragment Header contains an "Identification" field that, together with the IPv6 Source Address and the IPv6 Destination Address of a packet, identifies fragments that correspond to the same original datagram, such that they can be reassembled together by the receiving host. The only requirement for setting the Identification field is that the corresponding value must be different than that employed for any other fragmented datagram sent recently with the same Source Address and Destination Address. Some implementations use a simple global counter for setting the Identification field, thus leading to predictable Identification values. This document analyzes the security implications of predictable Identification values, and provides implementation guidance for setting the Identification field of the Fragment Header, such that the aforementioned security implications are mitigated. 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/rfc7739. Gont Informational [Page 1] RFC 7739 Implications of Predictable Fragment IDs February 2016 Copyright Notice Copyright (c) 2016 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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Security Implications of Predictable Fragment Identification Values . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Constraints for the Selection of Fragment Identification Values . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Algorithms for Selecting Fragment Identification Values . . . 8 5.1. Per-Destination Counter (Initialized to a Random Value) . 8 5.2. Randomized Identification Values . . . . . . . . . . . . 9 5.3. Hash-Based Fragment Identification Selection Algorithm . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . 13 7.2. Informative References . . . . . . . . . . . . . . . . . 14 Appendix A. Information Leakage Produced by Vulnerable Implementations . . . . . . . . . . . . . . . . . . 16 Appendix B. Survey of Fragment Identification Selection Algorithms Employed by Popular IPv6 Implementations 18 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 20 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20 Gont Informational [Page 2] RFC 7739 Implications of Predictable Fragment IDs February 2016 1. Introduction IPv6 specifies the Fragment Header, which is employed for the fragmentation and reassembly mechanisms. The Fragment Header contains an "Identification" field that, together with the IPv6 Source Address and the IPv6 Destination Address of a packet, identifies fragments that correspond to the same original datagram, such that they can be reassembled together by the receiving host. The only requirement for setting the Identification field is that itsShow full document text