iDefense released a security advisory for snort: http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=701 DESCRIPTION Remote exploitation of a design error vulnerability in Snort, as included in various vendors' operating system distributions, could allow an attacker to bypass filter rules. Due to a design error vulnerability, Snort does not properly reassemble fragmented IP packets. When receiving incoming fragments, Snort checks the Time To Live (TTL) value of the fragment, and compares it to the TTL of the initial fragment. If the difference between the initial fragment and the following fragments is more than a configured amount, the fragments will be silently discard. This results in valid traffic not being examined and/or filtered by Snort. ANALYSIS Exploitation of this vulnerability allows an attacker to bypass all Snort rules. In order to exploit this vulnerability, an attacker would have to fragment IP packets destined for a targeted host, ensuring that the TTL difference is greater than the configured maximum. By default, the maximum difference is 5. If an attacker is successful, all fragments with invalid TTL differences will be dropped. No rules will be applied to them. DETECTION iDefense has confirmed the existence of this vulnerability in Snort 2.8 and 2.6. Snort 2.4 is not vulnerable. WORKAROUND In the snort.conf file, set the ttl_limit configuration value to 255 as shown below. preprocessor frag3_engine: ttl_limit 255 This will set the allowable difference to the maximum possible value, and prevent fragments from being dropped. VENDOR RESPONSE Sourcefire has addressed this vulnerability by releasing version 2.8.1 of Snort. Upstream patches: http://cvs.snort.org/viewcvs.cgi/snort/ChangeLog.diff?r1=1.544&r2=1.545 (part) http://cvs.snort.org/viewcvs.cgi/snort/src/preprocessors/spp_frag3.c.diff?r1=1.50&r2=1.51 http://cvs.snort.org/viewcvs.cgi/snort/src/generators.h.diff?r1=1.63&r2=1.64 http://cvs.snort.org/viewcvs.cgi/snort/etc/gen-msg.map.diff?r1=1.43&r2=1.44 http://cvs.snort.org/viewcvs.cgi/snort/doc/README.frag3.diff?r1=1.7&r2=1.8 http://cvs.snort.org/viewcvs.cgi/snort/doc/snort_manual.tex.diff?r1=1.98&r2=1.99 + updated version of snort_manual.pdf Based on Detection part of the advisory, this should affect snort packages in F7 - F9, rawhide already has 2.8.1 which has changes above included.
snort-2.8.1-3.fc7 has been submitted as an update for Fedora 7
snort-2.8.1-3.fc8 has been submitted as an update for Fedora 8
snort-2.8.1-3.fc9 has been submitted as an update for Fedora 9
snort-2.8.1-3.fc9 has been pushed to the Fedora 9 stable repository. If problems still persist, please make note of it in this bug report.
snort-2.8.1-3.fc8 has been pushed to the Fedora 8 stable repository. If problems still persist, please make note of it in this bug report.
snort-2.8.1-3.fc7 has been pushed to the Fedora 7 stable repository. If problems still persist, please make note of it in this bug report.
This issue was addressed in: Fedora: https://admin.fedoraproject.org/updates/F7/FEDORA-2008-5045 https://admin.fedoraproject.org/updates/F8/FEDORA-2008-5001 https://admin.fedoraproject.org/updates/F9/FEDORA-2008-4986