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Date:      Thu, 20 Jan 2000 18:12:37 -0700
From:      Brett Glass <brett@lariat.org>
To:        Darren Reed <avalon@coombs.anu.edu.au>
Cc:        avalon@coombs.anu.edu.au (Darren Reed), imp@village.org (Warner Losh), jamiE@arpa.com (jamiE rishaw - master e*tard), tom@uniserve.com (Tom), mike@sentex.net (Mike Tancsa), freebsd-security@FreeBSD.ORG, freebsd-stable@FreeBSD.ORG, security-officer@FreeBSD.ORG
Subject:   Re: bugtraq posts: stream.c - new FreeBSD exploit?
Message-ID:  <4.2.2.20000120180821.0188d5c0@localhost>
In-Reply-To: <200001210103.MAA20844@cairo.anu.edu.au>
References:  <4.2.2.20000120174826.01882ad0@localhost>

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At 06:03 PM 1/20/2000 , Darren Reed wrote:

>If you're using "flags S keep state" or "flags S/SA keep state",
>then as far as I'm aware, having read the code, you are safe.

This might be a workaround. What rule(s) would have to follow it
to block the ACK?

>I'm intrigued to know what the bug is.  Reading the code, it is
>hard to see how you could make a box fall over using it, unless
>there were some serious problems in how random TCP ACK's were
>handled.

My guess is that there's a long code path, or other inefficiency, 
in the way the ACK is handled. Perhaps a linear search for the
right socket instead of one that's more clevery implemented
(e.g. search by port, then address, etc.).

--Brett



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