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Date: Fri, 01 Jun 2012 09:36:09 +0100
From: John Haxby <>
To: Kurt Seifried <>
Subject: Re: CVE Request -- kernel: tcp: drop SYN+FIN messages

Hash: SHA256

On 31/05/12 18:44, Kurt Seifried wrote:
> To clarify: CVE-2012-2663 is for the --syn processing flaw of SYN+FIN
> packets in iptables (user space tools). c
> Also if people could test their firewalls to make sure this still
> doesn't affect other operating systems that would probably be a good idea.

It's not clear to me why you would want to allow SYN+FIN at all.  So far
as I have been able to discover t is only used for T/TCP which was
obsoleted in May 2011 by RFC6247 which said this:

> 4. Security Considerations
> As mentioned in [RFC4614], the TCP Extensions for Transactions
> (T/TCP) [RFC1379][RFC1644] are reported to have security issues

RFC4614 has this to say:

> RFC 1379 I "Extending TCP for Transactions -- Concepts" (November
> 1992): found defective
> See RFC 1644.
> RFC 1644 E "T/TCP -- TCP Extensions for Transactions Functional
> Specification" (July 1994): found defective
> The inventors of TCP believed that cached connection state could
> have been used to eliminate TCP's 3-way handshake, to support
> two-packet request/response exchanges. RFCs 1379 [RFC1379] and
> 1644 [RFC1644] show that this is far from simple. Furthermore,
> T/TCP floundered on the ease of denial-of-service attacks that can
> result. One idea pioneered by T/TCP lives on in RFC 2140, in the
> sharing of state across connections.

I'm not averse to this being an iptables problem, I just wondered why
that is the case given the reasons for making T/TCP historic.


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