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Date: Fri, 03 Feb 2012 09:54:25 -0700
From: Kurt Seifried <>
CC: Marcus Meissner <>
Subject: Re: CVE Request (2002): Linux TCP stack could accept
 invalid TCP flag combinations

On 02/03/2012 03:37 AM, Marcus Meissner wrote:
> Hi,
> After a customer query likely coming from erroneous Security Scanner output,
> this issue from 2002 has no CVE id yet as far as I see:
> It describes a problem where firewalls might let some TCP flags combinations
> pass (e.g. all with RST flag set) and the OS (e.g. Linux) stack would in turn
> accept a TCP session it might not have accepted otherwise.
> The protection added in Linux 2.4.20 is checking for the RST (reset) flag
> when a SYN packet is received, which was I think the main attack scenario.
> The relevant part of the 2.4.20 patch is:
> @@ -3667,6 +3693,9 @@
>                 if(th->ack)
>                         return 1;
> +               if(th->rst)
> +                       goto discard;
> +
>                 if(th->syn) {
>                         if(tp->af_specific->conn_request(sk, skb) < 0)
>                                 return 1;
> The check still exists in current mainline git, so the issue is still fixed.
> Ciao, Marcus

Nice, a cert KB with a picture, never seen that before.

Please use CVE-2002-2438 for this issue.

Kurt Seifried Red Hat Security Response Team (SRT)

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