Snort mailing list archives
Is there a bug in "nocase"?
From: Jason Haar <Jason.Haar () trimble co nz>
Date: Fri, 30 May 2003 10:46:27 +1200
I'm trying to reduce the FPs on the Nimda rules (we run Snort over our WAN traffic - bl**dy great for picking up trojans). I've talked to the Samba group and came to the conclusion that at least for WinNT+, any reference to a "create filename" SMB call will always begin with the data stream 'content:"|ff 53 4d 42 a2|"' So I tried: alert tcp any any -> any 139 (msg:"NETBIOS nimda .EML"; \ content:"|ff 53 4d 42 a2|"; content:"|00|.|00|E|00|M|00|L|00 00|"; \ nocase; within:500; flow:established; classtype:bad-unknown; Note the "nocase". Then I copied a file "xxxx.eml" between two Win2K servers - it didn't trigger. I captured the transfer and ran "snort -v" over it, and that 'content' matched up - except the it was ".eml" instead of ".EML".... So then I added a new rule alert tcp any any -> any 139 (msg:"NETBIOS nimda .eml"; \ content:"|ff 53 4d 42 a2|"; content:"|00|.|00|E|00|M|00|L|00 00|"; \ nocase; within:500; flow:established; classtype:bad-unknown; ..and that caught it. Then I created a file "copy.EML" and copied that - the "NETBIOS nimda .eml" caught that one *instead of* the ""NETBIOS nimda .EML" one!!! So my question is: is "nocase" broken in the case where you "mix mode" it with HEX? It looks like it's only broken when you are nocasing capitals...???? Snort 2.0 under RH7.3 -- Cheers Jason Haar Information Security Manager, Trimble Navigation Ltd. Phone: +64 3 9635 377 Fax: +64 3 9635 417 PGP Fingerprint: 7A2E 0407 C9A6 CAF6 2B9F 8422 C063 5EBB FE1D 66D1 ------------------------------------------------------- This SF.net email is sponsored by: eBay Get office equipment for less on eBay! http://adfarm.mediaplex.com/ad/ck/711-11697-6916-5 _______________________________________________ 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://www.geocrawler.com/redir-sf.php3?list=snort-users
Current thread:
- Is there a bug in "nocase"? Jason Haar (May 29)