\-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-00:23 Security Advisory FreeBSD, Inc. Topic: Remote denial-of-service in IP stack [REVISED] Category: core Module: kernel Announced: 2000-06-19 Revised: 2000-07-11 Affects: FreeBSD systems prior to the correction date Credits: NetBSD Security Advisory 2000-002, and Jun-ichiro itojun Hagino Corrected: (Several bugs fixed, the date below is that of the most recent fix) 2000-06-08 (3.4-STABLE) 2000-06-08 (4.0-STABLE) 2000-06-02 (5.0-CURRENT) FreeBSD only: NO I. Background II. Problem Description There are several bugs in the processing of IP options in the FreeBSD IP stack, which fail to correctly bounds-check arguments and contain other coding errors leading to the possibility of data corruption and a kernel panic upon reception of certain invalid IP packets. This set of bugs includes the instance of the vulnerability described in NetBSD Security Advisory 2000-002 (see ftp://ftp.NetBSD.ORG/pub/NetBSD/misc/security/advisories/NetBSD-SA2000-002.txt.asc) as well as other bugs with similar effect. III. Impact Remote users can cause a FreeBSD system to panic and reboot. IV. Workaround Incoming packets containing IP Options can be blocked at a perimeter firewall or on the local system, using ipfw(8) (ipf(8) is also capable of blocking packets with IP Options, but is not described here). The following ipfw rules are believed to prevent the denial-of-service attack (replace the rule numbers '100'-'103' with whichever rule numbers are appropriate for your local firewall, if you are already using ipfw): ipfw add 100 deny log ip from any to any ipopt rr ipfw add 101 deny log ip from any to any ipopt ts ipfw add 102 deny log ip from any to any ipopt ssrr ipfw add 103 deny log ip from any to any ipopt lsrr Note that there are legitimate uses for IP options, although they are no believed to be in common use, and blocking them should not cause any problems. Therefore the log entries generated by these ipfw rules will not necessarily be evidence of an attempted attack. Furthermore, the packets may be spoofed and have falsified source addresses. V. Solution One of the following: 1) Upgrade your FreeBSD system to 3.4-STABLE, 4.0-STABLE or 5.0-CURRENT after the respective correction dates. 2) Apply the patch below and recompile your kernel. Either save this advisory to a file, or download the patch and detached PGP signature from the following locations, and verify the signature using your PGP utility. ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:23/ip_options.diff ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:23/ip_options.diff.asc # cd /usr/src/sys/netinet # patch -p < /path/to/patch_or_advisory [ Recompile your kernel as described in http://www.freebsd.org/handbook/kernelconfig.html and reboot the system ] VI. Revision History v1.0 2000-06-19 Initial release v1.1 2000-07-11 Note workaround using ipfw. Index: ip_icmp.c =================================================================== RCS file: /ncvs/src/sys/netinet/ip_icmp.c,v retrieving revision 1.39 diff -u -r1.39 ip_icmp.c \--- ip_icmp.c 2000/01/28 06:13:09 1.39 +++ ip_icmp.c 2000/06/08 15:26:39 @@ -662,8 +662,11 @@ if (opt == IPOPT_NOP) len = 1; else { \+ if (cnt < IPOPT_OLEN + sizeof(*cp)) \+ break; len = cp[IPOPT_OLEN]; \- if (len <= 0 || len > cnt) \+ if (len < IPOPT_OLEN + sizeof(*cp) || \+ len > cnt) break; } /* Index: ip_input.c =================================================================== RCS file: /ncvs/src/sys/netinet/ip_input.c,v retrieving revision 1.130 diff -u -r1.130 ip_input.c \--- ip_input.c 2000/02/23 20:11:57 1.130 +++ ip_input.c 2000/06/08 15:25:46 @@ -1067,8 +1067,12 @@ if (opt == IPOPT_NOP) optlen = 1; else { \+ if (cnt < IPOPT_OLEN + sizeof(*cp)) { \+ code = &cp[IPOPT_OLEN] - (u_char *)ip; \+ goto bad; \+ } optlen = cp[IPOPT_OLEN]; \- if (optlen <= 0 || optlen > cnt) { \+ if (optlen < IPOPT_OLEN + sizeof(*cp) || optlen > cnt) { code = &cp[IPOPT_OLEN] - (u_char *)ip; goto bad; } @@ -1174,6 +1178,10 @@ break; case IPOPT_RR: \+ if (optlen < IPOPT_OFFSET + sizeof(*cp)) { \+ code = &cp[IPOPT_OFFSET] - (u_char *)ip; \+ goto bad; \+ } if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) { code = &cp[IPOPT_OFFSET] - (u_char *)ip; goto bad; Index: ip_output.c =================================================================== RCS file: /ncvs/src/sys/netinet/ip_output.c,v retrieving revision 1.99 diff -u -r1.99 ip_output.c \--- ip_output.c 2000/03/09 14:57:15 1.99 +++ ip_output.c 2000/06/08 15:27:08 @@ -1302,8 +1302,10 @@ if (opt == IPOPT_NOP) optlen = 1; else { \+ if (cnt < IPOPT_OLEN + sizeof(*cp)) \+ goto bad; optlen = cp[IPOPT_OLEN]; \- if (optlen <= IPOPT_OLEN || optlen > cnt) \+ if (optlen < IPOPT_OLEN + sizeof(*cp) || optlen > cnt) goto bad; } switch (opt) { \-----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBOWuYHFUuHi5z0oilAQEp+wP/bK5jRQXK/d3sQw9cph/usAbiYUD6Ux3l MIo1R1ZPWnIE20Hx334hvr3u5AUnbtjkFg+86WZcpv5bgWjKS2VLyV4UjJIMMOQr sSDXta5X4XRO0aXv1Td/Jlkoh2UcoayhKssYa3LLwgcYq++BBGrwbJM+ShUGmllS qQ86FwHKdow= =5Ksz \-----END PGP SIGNATURE-----