Folks, We have published two new IETF I-Ds about fragmentation related security issues. They mostly focus on the countermeasures/mitigations, but it should be pretty obvious how you can exploit some of these vectors against e.g. otherwise *unfragmented* traffic (i.e., you should at the very least give this a thought, since it's likely to affect you). The first I-D is entitled "Security Implications of Predictable Fragment Identification Values" (http://tools.ietf.org/id/draft-gont-6man-predictable-fragment-id-00.txt). Its abstract is: ---- cut here ---- IPv6 specifies the Fragment Header, which is employed for the fragmentation and reassembly mechanisms. The Fragment Header contains an "Identification" field which, together with the IPv6 Source Address and the IPv6 Destination Address of the packet, identifies fragments that correspond to the same original datagram, such that they can be reassembled together at the receiving host. The only requirement for setting the "Identification" value is that it must be different than that of any other fragmented packet sent recently with the same Source Address and Destination Address. Some implementations simply use a global counter for setting the Fragment Identification field, thus leading to predictable values. This document analyzes the security implications of predictable Identification values, and updates RFC 2460 specifying additional requirements for setting the Fragment Identification, such that the aforementioned security implications are mitigated. ---- cut here ---- The second I-D is entitled 'Processing of IPv6 "atomic" fragments' (http://tools.ietf.org/id/draft-gont-6man-ipv6-atomic-fragments-00.txt). Its abstract is: ---- cut here ---- IPv6 allows packets to contain a Fragment Header, without the packet being actually fragmented into multiple pieces. Such packets typically result from 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 hosts as "fragmented traffic". By forging ICMPv6 "Packet Too Big" error messages an attacker can cause hosts to employ "atomic fragments", and the launch any fragmentation-based attacks against such traffic. This document discusses the generation of the aforementioned "atomic fragments", the corresponding security implications, and formally updates RFC 2460 and RFC 5722 such that the attack vector based on "atomic fragments" is completely eliminated. ---- cut here ---- Any feedback will be very appreciated. Thanks! Best regards, -- Fernando Gont SI6 Networks e-mail: fgont@xxxxxxxxxxxxxxx PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
