Snort mailing list archives
Re: many rules with good fast_pattern vs. single rule with pcre
From: "Joel Esler (jesler)" <jesler () cisco com>
Date: Mon, 29 Dec 2014 21:24:04 +0000
The answer is: It depends. How big are the packets? Is the pcre really simple, or it is it extremely complex? What is the prequalifying content match? Do you have a pcap? If so, you can test this.
On Dec 29, 2014, at 3:43 PM, Duane Howard <duane.security () gmail com> wrote: I'm writing some rules, and I find myself asking a question that's probably been answered, but my searching isn't turning up something obvious. In looking at a set of malware samples the only consistent pattern that can be used for all variants is a bunch of null bytes. This is a pretty poor fast pattern, and this alone makes for a large number of FP's. Adding another match to the rule can be done, but there are ~20 variants for the next byte match, these are good fast_pattern matches from my basic testing. My question, is whether it's better to have 20 rules with a good fast pattern, or one rule with a mediocre fast pattern and a pcre covering the 20 variants? This is another instance where I find myself wishing flowbits were taken into consideration *before* entering full rule evaluation, etc. ./d ------------------------------------------------------------------------------ Dive into the World of Parallel Programming! The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net_______________________________________________ Snort-users mailing list Snort-users () lists sourceforge net Go to this URL to change user options or unsubscribe: https://lists.sourceforge.net/lists/listinfo/snort-users Snort-users list archive: http://sourceforge.net/mailarchive/forum.php?forum_name=snort-users Please visit http://blog.snort.org to stay current on all the latest Snort news!
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------------------------------------------------------------------------------ Dive into the World of Parallel Programming! The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net
_______________________________________________ Snort-users mailing list Snort-users () lists sourceforge net Go to this URL to change user options or unsubscribe: https://lists.sourceforge.net/lists/listinfo/snort-users Snort-users list archive: http://sourceforge.net/mailarchive/forum.php?forum_name=snort-users Please visit http://blog.snort.org to stay current on all the latest Snort news!
Current thread:
- many rules with good fast_pattern vs. single rule with pcre Duane Howard (Dec 29)
- Re: many rules with good fast_pattern vs. single rule with pcre Joel Esler (jesler) (Dec 29)