Michael Rash, Security Researcher

IDS signature matching with iptables, psad, and fwsnort

IDS signature matching with iptables, psad, and fwsnort The UK's Unix & Open Systems User Group has re-printed an article I wrote originally for the December, 2007 security issue of USENIX ;login: Magazine The article is entitled "IDS signature matching with iptables, psad, and fwsnort" and concentrates on how to use the iptables infrastructure in the Linux kernel as a source of intrusion detection data. That is, iptables offers many features (such as application layer string matching) that allow a significant fraction of Snort rules to be converted into iptables rules, and fwsnort automates the conversion process. The end result is an iptables policy that is looking for evidence of malicious traffic. Also covered in the article is the concept of log analysis with an emphasis on passive OS fingerprinting. The completeness of the iptables logging format - which even includes the options portion of the TCP header when the --log-tcp-options argument is given on the iptables command line when building a LOG rule - allows psad to run the same algorithm that p0f uses to passively fingerprint remote operating systems.

In other news, Carla Schroder has written an article on psad for Enterprise Networking Planet. She recommends running psad alongside Snort, which falls nicely within the principle of defense-in-depth in order to maintain a strong defensive stance. Also, Noah Schiffman has written an article on port knocking for Network World. He mentions the usage of port knocking within some malware applications as an authentication mechanism, and he also touches on Single Packet Authorization.