Date: Wed, 30 May 2012 14:07:21 -0600 From: Kurt Seifried <kseifried@...hat.com> To: oss-security@...ts.openwall.com CC: John Haxby <john.haxby@...cle.com> Subject: Re: CVE Request -- kernel: tcp: drop SYN+FIN messages -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 05/30/2012 12:48 PM, John Haxby wrote: > > On 30 May 2012, at 19:25, Florian Weimer wrote: > >> * John Haxby: >> >>> Recently we have a couple of queries relating to a Nessus >>> "TCP/IP SYN+FIN Packet Filtering Weakness". This has not been >>> helped by the fact that  actually points (indrectly) to >>> CVE-2002-2438 which is actually a SYN+RST problem. >> >> Reading the discussion here, >> >> <http://comments.gmane.org/gmane.linux.network/213981> >> >> it seems to me that this is just a performance optimization >> which could be bypassed by using different flags, so I don't >> think there's a vulnerability or fix here, except the general >> lack of source IP address validation in IP networks. > > That's the same thread that I referred to but I didn't reach the > same conclusion that you did. It is possible to block SYN+FIN in > iptables, but the distros I'm aware of don't have that kind of > check in place so people will be vulnerable to this kind of DoS. > > The conclusion from the thread was that SYN+FIN is not a legitimate > packet so the kernel should drop it. The nessus people seem to > think the same thing: they have a test for this (although they > refer to the SYN+RST fix from a decade ago). If there's a > consensus that we don't need a CVE then we can go to nessus and > have them fix, remove or update their test. > > One could argue that if SYN+FIN doesn't need a CVE then SYN+RST > didn't either since it can be blocked by the same, or very similar, > iptables rule. > > jch No this definitely gets a CVE (see previous email), it directly bypasses a security mechanism that is documented (man iptables, --syn section), and other parts of iptables do handle it correctly as far as I can tell (e.g. --state NEW). It allows bypass of firewall rules as documented, so if that doesn't get a CVE then nothing the world has gone upside down =). - -- Kurt Seifried Red Hat Security Response Team (SRT) PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQIcBAEBAgAGBQJPxn35AAoJEBYNRVNeJnmT1OgP/0q1axsnDoz7OhjNW5Cjzo9f x0H72pYGOm3J/luxpCX78/Myzs+YubPkkmYrg37QCZpKJQXljGMRlyNNvDrkUo+C adeZH5vGIqD2uNwUmFmqPIf5WZezaWBXj1wdVAAk67rF6w4y31u2VJFj3Lytuq1z 3xelQl8qfdj8UTOB3+4MMGuuMX8udCMcER+6JgtdaunVXqxppqICk7BLANJbWAPG jCPi8HcVp8NYpvwjhMW4ezLlMPls64Bq4Ar47woOyycYYgjBobSzCID5yhqvzLX8 dXA2Hi/6B6G1xPlrwVjAPfUcnD8H9TJAzRGtZU0LfN2UaY/x3F3Pt1tpdZN1u2yB SzRnn2ko+rXTrOXF97gW8IrgvPnw9Zai2GsPoVjZAcN2zAHfLirfgq3gM3ZCV68/ u5tMdk/+mEJ3K/Haspr6o09c0G6k6hZuU9JDqUaKW3kfyTeYUcOSyJarpI+nDkOy lyKhgOHrgw6B8D5itdJXH4VZoa6eMygFlCU9AanPxn/1bhEgBv4Tr7Jke8dnd6uZ gByj+mC50ShDMOpCNfsc+8Xpqy5PahwH1zD1P5SPJgJJ9dCTM8JHdzBsJe3AykL+ snJBYSQ65VwmTkDH4/vgtWKqzsXjNuWvsU5ZyIuy4sjWs1uHUIVvIARSTuoAj3Ql 72aYlQSD704yaxxa6rnW =Uq2f -----END PGP SIGNATURE-----
Powered by blists - more mailing lists
Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.