[Bro] Questions about signature regexes

Robin Sommer robin at icir.org
Sat Jan 28 20:23:12 PST 2006

On Sat, Jan 28, 2006 at 19:00 +0000, you wrote:

> - Are they PCREs? I see a lot of "# Not supported: pcre" in

They are regexps but not PCREs; they use Bro's syntax which is
slightly different.

(That reminds me that I've a prototypical pcre->bro converter lying
around somewhere. But actually there doesn't seem to be much
interest in automatically converting Snort sigs these days.)

> - When I want a pattern to match at the beginning of the payload, I
> presume I have to say "payload /^", right?

Right. Alternatively you can just leave the "^" out as the regexps
are implictly anchored at the first byte. To match at arbitrary
positions, a wildcard is required, e.g., "/.*foo/.

> - Can I match on fixed TCP stream content of a given length by giving
> the whole string surrounded by ^ and $, i.e., this:



Robin Sommer * Phone +1 (510) 666-2886 * robin at icir.org 
ICIR/ICSI    * Fax   +1 (510) 666-2956 *   www.icir.org

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