FreeBSD Security Officer
1998-Nov-04 11:37 UTC
FreeBSD Security Advisory: FreeBSD-SA-98:08.fragment
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============================================================================FreeBSD-SA-98:08
Security Advisory
FreeBSD, Inc.
Topic: IP fragmentation denial of service
Category: core
Module: kernel
Announced: 1998-11-04
Affects: FreeBSD 3.0 and
FreeBSD-current before the correction date.
Corrected: FreeBSD-3.0 and FreeBSD-current as of 1998/10/27
FreeBSD only: Yes
Patches: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:08/
I. Background
IP connections are controlled through a series of packets that are
received by the two computers involved in the connection.
When packets are too large to be sent in a single IP packet (due to
interface hardware limitations for example), they can be fragmented
(unless prohibited by the Don't Fragment flag).
The final destination will reassemble all the fragments of an IP packet
and pass it to higher protocol layers (like TCP or UDP).
II. Problem Description
There is a bug in the IP fragment reassembly code that might lead
to a kernel panic. An attacker can create and send a pair of
malformed IP packets which are then reassembled into an invalid
UDP datagram. Such an UDP datagram would then cause a server to
panic and crash.
III. Impact
When this bug is exploited the operating system will panic. This results
in a reboot of the system.
This vulnerability has been discussed in public security forums and
exploit programs are circulating to take advantage of this bug.
IV. Workaround
None.
V. Solution
Index: ip_input.c
================================================================== RCS
file: /home/cvsup/freebsd/CVS/src/sys/netinet/ip_input.c,v
retrieving revision 1.102
retrieving revision 1.103
diff -u -u -r1.102 -r1.103
--- ip_input.c 1998/10/16 03:55:01 1.102
+++ ip_input.c 1998/10/27 09:11:41 1.103
@@ -750,7 +750,7 @@
* if they are completely covered, dequeue them.
*/
for (; q != NULL && ip->ip_off + ip->ip_len >
GETIP(q)->ip_off;
- p = q, q = nq) {
+ q = nq) {
i = (ip->ip_off + ip->ip_len) -
GETIP(q)->ip_off;
if (i < GETIP(q)->ip_len) {
============================================================================FreeBSD,
Inc.
Web Site: http://www.freebsd.org/
Confidential contacts: security-officer@freebsd.org
Security notifications: security-notifications@freebsd.org
Security public discussion: freebsd-security@freebsd.org
PGP Key: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc
Notice: Any patches in this document may not apply cleanly due to
modifications caused by digital signature or mailer software.
Please reference the URL listed at the top of this document
for original copies of all patches if necessary.
============================================================================
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