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OpenBSD Kernel Panic While Processing IPSec Link2 Option
------------------------------------------------------------------------
SUMMARY
A bug in the way the OpenBSD kernel handles ICMP packets while the link2
option is set for IPSec processing leaves the system vulnerable to a
single ICMP packet attack able to crash the kernel.
DETAILS
Vulnerable Systems:
* OpenBSD version 3.5
An OpenBSD system configured as a gateway between two networks might be
vulnerable to a specific attack that can crash the kernel if bridging is
enabled and the link2 option is given for IPSec processing. In an event
that a malformed ICMP echo request packet arrives from a host on network A
with a destination of a host on network B, the OpenBSD kernel will crash
and cause a kernel panic.
No core file is generated. If the DDB_PANIC option is set, the machine
reboots upon receipt of the ICMP echo request. The commands that lead to
the vulnerable situations are as follows:
# ifconfig bridge0 create
# brconfig bridge0 add fxp0 add fxp1 up
# brconfig bridge0 link2
Naturally, in order to configure the system in such a manner, a user would
have to have root access on the system.
The problem was observed on a test network and was reproduced as well on a
VMWare network.
Patch Availability:
The OpenBSD team was contacted and a patch was introduced to the CVS
within 12 hours, an errata is available at:
<http://www.openbsd.org/errata34.html>
http://www.openbsd.org/errata34.html. The patch code is listed below and
is also available from
<ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.4/common/028_bridge.patch>
ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.4/common/028_bridge.patch:
Index: sys/net/if_bridge.c
===================================================================
RCS file: /cvs/src/sys/net/if_bridge.c,v
retrieving revision 1.136
diff -u -r1.136 if_bridge.c
--- sys/net/if_bridge.c 21 Jun 2004 23:50:36 -0000 1.136
+++ sys/net/if_bridge.c 18 Aug 2004 09:29:04 -0000
@@ -2275,9 +2275,9 @@
splx(s);
return (1);
} else {
+ splx(s);
skiplookup:
/* XXX do an input policy lookup */
- splx(s);
return (0);
}
} else { /* Outgoing from the bridge. */
ADDITIONAL INFORMATION
The information has been provided by <mailto:vafa@hush.ai> Vafa Izadinia.
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