Technical Summary:
The IPv6 specification allows packets to contain a Fragment Header
without the packet being actually fragmented into multiple pieces (we
refer to these packets as "atomic fragments"). Such packets are
typically sent by hosts that have received an ICMPv6 "Packet Too Big"
error message that advertises a "Next-Hop MTU" smaller than 1280
bytes, and are currently processed by some implementations as normal
"fragmented traffic" (i.e., they are "reassembled" with any other
queued fragments that supposedly correspond to the same original
packet). Thus, an attacker can cause hosts to employ "atomic
fragments" by forging ICMPv6 "Packet Too Big" error messages, and
then launch any fragmentation-based attacks against such traffic.
This document discusses the generation of the aforementioned "atomic
fragments" and the corresponding security implications.
Additionally, this document formally updates RFC 2460 and RFC 5722
such that IPv6 atomic fragments are processed independently of any
other fragments, thus completely eliminating the aforementioned
attack vector.
Working Group Summary:
There is working group support for this document. It has been discussed on the
mailing list and in face-to-face 6man sessions. The chairs did a review
that improved the quality of the document.
Document Quality:
The document includes an appendix that lists implementations that generate
atomic fragments and/or implement this document.
Personnel:
Bob Hinden, Document Shepherd
Brian Haberman, Internet AD