[Snort-sigs] PCRE /PR modifiers

Y M snort at ...3751...
Tue Jul 7 13:56:42 EDT 2015


Hi,
According to the documentation (http://manual.snort.org/node32.html#pcre-mod_snort), the PCRE modifiers P and R can be used to match content in HTTP request body in a relative manner and are similar to http_client_body and distance:0, respectively. 
While testing with a rule that uses both PCRE modifiers, I kept receiving the below error:
PCRE unsupported configuration : both relative & uri options specified
Not sure why the error refers to uri options, although the rule did not involve any uri content modifiers. For example, assume the following HTTP request bodies from different sessions:
ABC:doAABC:doBABC:doC
What I have been testing was something like:
content:"ABC|3A|"; http_client_body; pcre:"/(doA|doB|doC)/PR"; and this is where I got the error.
Does this mean that the PCRE "R" modifier works only with uri content matches, or is it because the "P" modifier matches the unnormalized HTTP body? This was strange to me because while testing I recall that using relative matches with http_client_body (ie.: not using PCRE) and distance:0 works just fine.
Thanks.YM 		 	   		  
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