From security-advisories@FreeBSD.org Tue Apr 17 06:41:30 2001 From: FreeBSD Security Advisories To: BUGTRAQ@SECURITYFOCUS.COM Date: Mon, 16 Apr 2001 12:37:22 -0700 Subject: [BUGTRAQ] FreeBSD Security Advisory FreeBSD-SA-01:32.ipfilter -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-01:32 Security Advisory FreeBSD, Inc. Topic: IPFilter may incorrectly pass packets Category: core Module: IPFilter Announced: 2001-04-16 Credits: Thomas Lopatic Affects: FreeBSD 3.x (all releases), FreeBSD 4.x (all releases), FreeBSD 3.5-STABLE, and 4.2-STABLE prior to the correction date. Corrected: 2001-04-07 (FreeBSD 4.2-STABLE) Vendor status: Corrected FreeBSD only: NO I. Background IPFilter is a multi-platform packet filtering package. II. Problem Description When matching a packet fragment, insufficient checks were performed to ensure the fragment is valid. In addition, the fragment cache is checked before any rules are checked. Even if all fragments are blocked with a rule, fragment cache entries can be created by packets that match currently held state information. Because of these discrepancies, certain packets may bypass filtering rules. All versions of FreeBSD prior to the correction date, including FreeBSD 3.5.1 and 4.2, contain this problem. The base system that will ship with FreeBSD 4.3 does not contain this problem since it was corrected during the beta cycle before the release. III. Impact Malicious remote users may be able to bypass filtering rules, allowing them to potentially circumvent the firewall. IPFilter is not enabled by default. If you have not enabled IPFilter, your system is not vulnerable to this problem. IV. Workaround Since fragment cache matching occurs before filtering rules checking, it is not possible to work around this problem using IPFilter rules. V. Solution [FreeBSD 3.x] Due to the age of the IPFilter package shipped with FreeBSD 3.x, it is recommended that FreeBSD 3.x systems update to IPFilter 3.4.17 using the package available from the authors website: http://coombs.anu.edu.au/~avalon/ip-filter.html [FreeBSD 4.x] One of the following: 1) Upgrade to FreeBSD 4.2-STABLE after the correction date. 2) Download the patch and detached PGP signature from the following location: The following patch applies to FreeBSD 4.1-RELEASE through 4.2-STABLE. # fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:33/ipfilter.patch # fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:33/ipfilter.patch.asc Verify the detached signature using your PGP utility. Issue the following commands as root: # cd /usr/src # patch -p < /path/to/patch If the system is using ipfilter as a kernel module, the module may be rebuilt and installed and ipfilter rules reloaded with the following commands: # cd /usr/src/sys/modules/ipfilter # make all install # kldunload ipl && kldload ipf && ipf -Fa -f /etc/ipf.rules Otherwise, if ipfilter is compiled into the kernel, a new kernel will need to be compiled and installed and the system will have to be rebooted for the changes to take effect. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.4 (FreeBSD) Comment: For info see http://www.gnupg.org iQCVAwUBOttI71UuHi5z0oilAQHKwwP8CfuhsJA8z78zOJCLSGWPAJSgsi9aFvP7 oVd4eKkVHgHI5hC5QTRgOGg84KncXUu7DJjlOlZ+6nVxcxdp4DED/yRTWjqc14og guP3SBAcJwH5y44ZW/VV+LlbNJue77Igkq1u3dran6TPBMdiUeRIRsj0acn6k1nc ATwy7N0Ade8= =Wujh -----END PGP SIGNATURE-----