full-disclosure - Core Internet Vulnerable

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From: peak at argo.troja.mff.cuni.cz (Pavel Kankovsky)
Subject: Core Internet Vulnerable - News at 11:00

On Tue, 20 Apr 2004, Michal Zalewski wrote:

> That said, kudos to Watson: it is definitely good to see this problem
> being finally discussed in broad daylight; I think it would be good to see
> some kludges intended to mitigate it a bit.

Data injection may be thwarted by TCP timestamps (RFC 1323). Timestamps
are 32-bits long and received echoed timestamps must correspond to
(recently) sent timestamps. The exact implementation would probably be
somewhat tricky but I think it might be able to extend the "effective
sequence number" by at least 16 bits.

A spoofed "timestamp-less" SYN or SYN-ACK packet during the initial 3-way
handshake might prevent the use of TCP timestamps but an attacker would
have to guess full 32 bits of an ISN (or of two ISNs in the SYN-ACK case).

Unfortunately timestamps won't help against spoofed RST packets because
existing TCP implementations are supposed not to send them in RST
packets.

--Pavel Kankovsky aka Peak  [ Boycott Microsoft--http://www.vcnet.com/bms ]
"Resistance is futile. Open your source code and prepare for assimilation."