Bugtraq: re:Breaking the checksum (a new TCP/IP blind data injection technique

[Michal Zalewski <lcamtuf () ghettot org>]

On Mon, 15 Dec 2003 LARSJ () inel gov wrote:

> This is a good line of thought that needs to be re-addressed every now
> and then, but I can remember discussing this exact attack ten years ago.
> There's even an RFC on it. RFC 1858 if memory serves.
Lars,

Nope. The set of attacks discussed in RFC1858 is indeed old, but has
nothing to do with the TCP/IP injection vector I have described. The
RFC1858 attacks describe firewall-bypassing attacks: "tiny fragment
attack", where a malicious TCP or UDP packet is sent in chunks too small
to be properly analyzed by the device; and "source porting", where the
header of a previously analyzed packet is modified by an overlapping
chunk.

Both techniques are old, well known and easy to prevent (and, indeed,
prevented by all modern implementations). The attack I described, for a
change, is not aimed at bypassing a firewall, and seems to be pretty damn
impossible to fix without breaking some functionality.

Cheers,
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 Michal Zalewski * [http://lcamtuf.coredump.cx]
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