oss-security - CVE Request -- kernel: tcp: drop SYN+FIN messages

Follow @Openwall on Twitter for new release announcements and other news

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date: Wed, 30 May 2012 10:44:43 +0100
From: John Haxby <john.haxby@...cle.com>
To: oss-security@...ts.openwall.com
Subject: CVE Request -- kernel: tcp: drop SYN+FIN messages


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

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 [1] actually points (indrectly) to CVE-2002-2438 which is
actually a SYN+RST problem.

The Nessus script actually appears to detect this problem (also
described in [2]):

commit fdf5af0daf8019cec2396cdef8fb042d80fe71fa
Author: Eric Dumazet <eric.dumazet@...il.com>
Date:   Fri Dec 2 23:41:42 2011 +0000

    tcp: drop SYN+FIN messages
   
    Denys Fedoryshchenko reported that SYN+FIN attacks were bringing his
    linux machines to their limits.
   
    Dont call conn_request() if the TCP flags includes SYN flag
   
    Reported-by: Denys Fedoryshchenko <denys@...p.net.lb>
    Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 78dd38c..0cbb440 100644
- --- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5811,6 +5811,8 @@ int tcp_rcv_state_process(struct sock *sk, struct
sk_buff *skb,
             goto discard;
 
         if (th->syn) {
+            if (th->fin)
+                goto discard;
             if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
                 return 1;
 

References:
[1] http://www.nessus.org/plugins/index.php?view=single&id=11618
[2] http://markmail.org/thread/l6y5vu3tub434z4w
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.12 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iF4EAREIAAYFAk/F7AoACgkQRQu7fpQvo8iHgwD+K4uHEOheYdcAopAYWUDystWm
KfrN/P2vvbM8vJ7PxvYA/3WX3KE87EdiGScqhZWXI0/A1PPe+yTVM5+1iwqCR4hk
=OtXl
-----END PGP SIGNATURE-----

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.