cipherdyne.org

28 April, 2012

The 1.6.2 release of fwsnort is available for download. The most impactful change in this release is a switch to how fwsnort loads translated rules into the running iptables policy. Instead of attempting to parse the local policy and only add those rules in that appear to match protocols that the policy allows, fwsnort now loads all translated rules by default. The reasoning for this change is in the ChangeLog below. There are a few bug fixes and updates to get fwsnort working without warnings on recent versions of perl as well as an ICMP type fix for recent versions of iptables. As usual, please let me know if there are any issues.

Here is the complete fwsnort-1.6.2 ChangeLog:

• Switched --no-ipt-sync to default to not syncing with the iptables policy. By default fwsnort attempts to match translated Snort rules to the running iptables policy, but this is tough to do well because iptables policies can be complex. And, before fwsnort switched to the iptables-save format for instantiating the policy, a large set of translated rules could take a really long time to make active within the kernel. Finally, many Snort rules restrict themselves to established TCP connections anyway, and if a restrictive policy doesn't allow connections to get into the established state for some port let's say, then there is little harm in having translated Snort rules for this port. Some kernel memory would be wasted (small), but no performance would be lost since packets won't be processed against these rules anyway. The end result is that the default behavior is now to not sync with the local iptables policy in favor of translating and instantiating as many rules as possible.
• Replaced Net::IPv4Addr with the excellent NetAddr::IP module which has comprehensive support for IPv6 address network parsing and comparisons.
• Moved the fwsnort.sh script and associated files into the /var/lib/fwsnort/ directory. This was suggested by Peter Vrabec.
• Bug fix for recent versions of iptables (such as 1.4.12) where the icmp match requires --icmp-type to be set - some Snort rules look for a string to match in icmp traffic, but don't also specify an icmp type.
• Bug fix for 'qw(...) usage as parenthesis' warnings for perl > 5.14
• Removed the ExtUtils::MakeMaker RPM build requirement from the fwsnort.spec file. This is a compromise which will allow the fwsnort RPM to be built even if RPM doesn't or can't see that ExtUtils::MakeMaker is installed - most likely it will build anyway. If it doesn't, there are bigger problems since fwsnort is written in perl. If you want to build the fwsnort RPM with a .spec file that requires ExtUtils::MakeMaker, then use the "fwsnort-require-makemaker.spec" file that is bundled in the fwsnort sources.