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Date: Tue, 29 May 2012 11:02:42 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
CC: John Haxby <john.haxby@...cle.com>, Marcus Meissner <meissner@...e.de>
Subject: Re: CVE Request (2002): Linux TCP stack could accept
 invalid TCP flag combinations

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On 05/29/2012 06:17 AM, John Haxby wrote:
> On 03/02/12 10:37, 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:
>> 
>> http://www.kb.cert.org/vuls/id/464113

Nope it lists one at the bottom:

Other Information
CVE IDs: CVE-2002-2438

>> 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
> 
> I suspect that this actually came from here:
> 
> http://www.nessus.org/plugins/index.php?view=single&id=11618
> 
> It's entirely possible that there's a typo in the web page because
> it talks about TCP+FIN but refers to web pages dealing with the
> much older TCP+RST.
> 
> There is actually a SYN+FIN discard fix in the mainline kernel
> which would appear to be a DoS ("Denys Fedoryshchenko reported that
> SYN+FIN attacks were bringing his linux machines to their limits.")
> should we have a CVE for this issue?  (I'll ask in a separate
> message if so.)
> 
> jch

Can you send a separate message and specific information? Thanks.


- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993

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