Saturday, April 21, 2007

fwsnort-1.0 release

The 1.0 release of fwsnort is ready for download. This release is a major update that adds the ability to build an iptables policy against the NFQUEUE or QUEUE targets in order to perform preliminary content matching in the Linux kernel using the iptables string match extension. Here is the full ChangeLog:

  • Major update to include support for the NFQUEUE and QUEUE targets with new command line options --NFQUEUE and --QUEUE. This changes the default LOG target to the NFQUEUE or QUEUE targets instead, and at the same time builds a parallel Snort rule set in the /etc/fwsnort/snort_rules_queue directory. Every Snort rule in this directory has at least one "content" keyword, which fwsnort uses in the resulting iptables policy. This policy only sends those packets to snort_inline via the NFQUEUE or QUEUE target that match a content field within some Snort rule. The end result is that snort_inline should run faster because the vast majority of packets (which are not malicious) are processed via the Linux kernel without ever having to be sent to userspace for analysis. There is a tradeoff here in terms of attack detection; snort_inline does not receive all packets associated with a stream, so it cannot detect attacks quite as effectively (snort_inline does not have an opportunity to look at reassembled buffers). However, this trade off may be acceptable for large sites where performance is more important.
  • Bug fix to remove any existing jump rules from the built-in INPUT, OUTPUT, and FORWARD chains before creating a new jump rules. This allows the script to be executed multiple times without creating a new jump rule into the fwsnort chains for each execution.
  • Added the -X command line argument to allow fwsnort to delete all of the fwsnort chains; this emulates the iptables command line argument of the same name.
  • Minor output enhancements and bugfixes to give more insight into the translation process. For example, if fwsnort is run in --snort-sid mode but is unable to translate the specified signatures, the user is notified. Also, any existing /etc/fwsnort/ script is not archived and erased until fwsnort is actually going to write a new one.
  • Added sid values to iptables comment match string.
  • Bugfix for iptables string match --from and --to values to skip past packet headers. This is an approximation until a new --payload option can be added to the string match extension.
  • Added a single iptables rule testing API internally within fwsnort; this adds a measure of consistency and removes some duplicate code.
  • Added fwsnort mailing list at SourceForge.

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