-----BEGIN PGP SIGNED MESSAGE----- =============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : Xander Jansen Index : S-98-72 Distribution : World Page : 1 Classification: External Version: 1 Subject : FreeBSD IP fragmentation denial of service Date : 6-Nov-98 =============================================================================== By courtesy of FreeBSD inc. we received the following information. FreeBSD inc. Advisory SA-98:08 reports a vulnerability regarding to IP fragmentation denial of service. CERT-NL recommends implementing the solution outlined in section V. ============================================================================= 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. ============================================================================= =============================================================================== CERT-NL is the Computer Emergency Response Team for SURFnet customers. SURFnet is the Dutch network for educational, research and related institutes. CERT-NL is a member of the Forum of Incident Response and Security Teams (FIRST). All CERT-NL material is available under: http://www.surfnet.nl/surfnet/security/cert-nl.html ftp://ftp.surfnet.nl/surfnet/net-security In case of computer or network security problems please contact your local CERT/security-team or CERT-NL (if your institute is NOT a SURFnet customer please address the appropriate (local) CERT/security-team). CERT-NL is one/two hour(s) ahead of UTC (GMT) in winter/summer, i.e. UTC+0100 in winter and UTC+0200 in summer (DST). Email: cert-nl@surfnet.nl ATTENDED REGULARLY ALL DAYS Phone: +31 302 305 305 BUSINESS HOURS ONLY Fax: +31 302 305 329 BUSINESS HOURS ONLY Snailmail: SURFnet bv Attn. CERT-NL P.O. Box 19035 NL - 3501 DA UTRECHT The Netherlands NOODGEVALLEN: 06 52 87 92 82 ALTIJD BEREIKBAAR EMERGENCIES : +31 6 52 87 92 82 ATTENDED AT ALL TIMES CERT-NL'S EMERGENCY PHONENUMBER IS ONLY TO BE USED IN CASE OF EMERGENCIES: THE SURFNET HELPDESK OPERATING THE EMERGENCY NUMBER HAS A *FIXED* PROCEDURE FOR DEALING WITH YOUR ALERT AND WILL IN REGULAR CASES RELAY IT TO CERT-NL IN AN APPROPRIATE MANNER. CERT-NL WILL THEN CONTACT YOU. =============================================================================== -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 5.5.3i for non-commercial use iQCVAwUBNkLRO1pSTqmIRWKVAQHurgP9EDq6RCGqgnRFSVfPS9yld+Ki+16KUs5i W/8NxiBqKZ7KrM+WNTl+mTUe+lf3R9DjQSQ7M4UFzAduCLxPmX+oe84jgCiOrRin okqXSNqKxKanERn6tfPvWfWphyW1d9juN1BD9j7OpswaRd4G18N5duQ85Ddcxt6G jqqx3ZqgKkI= =/92P -----END PGP SIGNATURE----- -- End --