AusCERT - ESB-98.169 -- FreeBSD Security Advisory: FreeBSD-SA-98:08 -- IP fragmentation denial of service

HOME
About AusCERT
Membership
PKI Services
Training
Publications
Sec. Bulletins
Conferences
News & Media
Services
Web Log
Site Map
Site Help
Member login
ESB-98.169 -- FreeBSD Security Advisory: FreeBSD-SA-98:08 -- IP fragmentation denial of service
Date: 05 November 1998

Click here for printable version
-----BEGIN PGP SIGNED MESSAGE-----

===========================================================================
              AUSCERT External Security Bulletin Redistribution
                                    
          ESB-98.169 -- FreeBSD Security Advisory: FreeBSD-SA-98:08
                     IP fragmentation denial of service
                                    
                               05 November 1998

===========================================================================

The FreeBSD Security Team has released the following advisory concerning
a vulnerability 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 that can
cause a server to panic and crash.


- ---------------------------BEGIN INCLUDED TEXT------------------


- -----BEGIN PGP SIGNED MESSAGE-----

=============================================================================
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.
=============================================================================


- -----BEGIN PGP SIGNATURE-----
Version: 2.6.3ia
Charset: noconv

iQCVAwUBNkCrf1UuHi5z0oilAQE0GgQAga3x91fd4QU8/vXKkPp8h2hUmHifhdIc
K4PynSKtqP8IQFzMzGApMU5MLCV2s6cXLj2cznAuCcHiF6xWsTIf1JoqgtaYZaTS
pBtW9Dxp+5OYlVnGHfijUbO8sop2PpAqaBpVv2CnxYvFz3sMbM8z1H7wkWEHvL7Z
MHXYAJ2Apfk=
=fOyn
- -----END PGP SIGNATURE-----


- ---------------------------END INCLUDED TEXT--------------------

This security bulletin is provided as a service to AusCERT's members.  As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content.  The decision to use any or all of this information is
the responsibility of each user or organisation, and should be done so in
accordance with site policies and procedures.

NOTE: This is only the original release of the security bulletin.  It will
not be updated when updates to the original are made.  If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the original authors to ensure that the information is still current.

Contact information for the authors of the original document is included
in the Security Bulletin above.  If you have any questions or need further
information, please contact them directly.

Previous advisories and external security bulletins can be retrieved from:

        http://www.auscert.org.au/Information/advisories.html

If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for emergencies.

-----BEGIN PGP SIGNATURE-----
Version: 2.6.3i
Charset: noconv
Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key

iQCVAwUBNmUyASh9+71yA2DNAQHvigQAnD4c0f/eiezo+SBv0pYfLI2SZhpkg9l7
I/dnLhO3FEpQkZVMShfqDGUZd+9QVnxsyE8/HB3SxHaTG5XNj6Ub24F+GIcqE+qd
TIfpCzoH/1SrPjJSluVs1CAVN+F5ruEfggXuNJQvM0+FIlwojF9KfC95zKCWw9EM
MeZ/X//171Y=
=8aBz
-----END PGP SIGNATURE-----