Re: PIX responding with SYN+ACK to SYN+ACK probe sent on open port

On Wed, Jan 12, 2005 at 02:52:59PM +0100, stephane nasdrovisky wrote:

> In general, an implementation must be conservative in its sending
> behavior, and liberal in its receiving behavior.

Are we still talking about firewalls? ;-)

Related reading:
http://lists.megacity.org/pipermail/rfci-discuss/2004-September/002758.html

IMO, ignoring ACK flag in SYN packet is against TCP spec, not just
"liberal" acceptance in the mean of "not object to technical errors
where the meaning is still clear" (the same paragraph you are
quoting). It also poses some security risks, anyway...

Martin Mačok
ICT Security Consultant
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Received on Jan 14 2005