01-22-2004 12:24 PM - edited 03-09-2019 06:12 AM
I need some remedial help on the use of regular expressions in built-in sigs.
In particular, I am referring to the expressions used in Sig 3115 (Sendmail Header Overflow). I am seeing many false positives and I am trying to figure out just what the signature is looking for.
These are the expressions:
(\x3c>){20}
\x26lt;>\x26lt;>\x26lt;>...
Can you help?
Thanks,
Don
Solved! Go to Solution.
01-22-2004 03:30 PM
From your expressions above, I presume that you're using 4.x sensors and looking for subsignature 3 of signature 3115. This signature is looking for the following:
(<>){20}
This is basically "<><><>..." repeated 20 or more times. "(\x3c>){20}" is the same thing as above. \x3c is the same as "<". We had to do this because of a regex quirk. The "\x26lt;>\x26lt;>\x26lt;>..." should look like "<><><>...". This is a victim of our XML data file which can't handle certain characters properly. This is a display bug. I'll look into getting this fixed.
In regards to the false positives, if you can capture some iplogs and send them to mcerha@cisco.com, I will look into the cause. I'd have to see the traffic to tell what exactly is going on.
01-22-2004 03:30 PM
From your expressions above, I presume that you're using 4.x sensors and looking for subsignature 3 of signature 3115. This signature is looking for the following:
(<>){20}
This is basically "<><><>..." repeated 20 or more times. "(\x3c>){20}" is the same thing as above. \x3c is the same as "<". We had to do this because of a regex quirk. The "\x26lt;>\x26lt;>\x26lt;>..." should look like "<><><>...". This is a victim of our XML data file which can't handle certain characters properly. This is a display bug. I'll look into getting this fixed.
In regards to the false positives, if you can capture some iplogs and send them to mcerha@cisco.com, I will look into the cause. I'd have to see the traffic to tell what exactly is going on.
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide