Snort mailing list archives

Re: Snort doesn't trigger while the payload size is big (even for ~4-5KB files)

From: Joel Esler <jesler () sourcefire com>
Date: Sun, 5 Dec 2010 12:22:41 -0500

Can you provide your Snort configuration, rule you are trying to write
and a full session pcap of the traffic you are attempting to detect?

On Sunday, December 5, 2010, Sujit Ghosal <thesujit () gmail com> wrote:

Hi All,    I had a similar type of issue some days back to detect any server side/client side vulnerabilities as 
Snort was not detecting even for a single GET or <html> pattern in any requests/responses respectively. Anyways the 
problem is somehow solved. It just suddenly started working (may be I think my firewall was blocking initially, I am 
not fully sure though).

    Now I came through a very bizzare problem. While I am writing a client side signature (lets say some PDF 
vulnerability signatures). If the PDF has less number of bytes (within 500-600 bytes and the whole PDF is of 600 
bytes) and attack pattern comes within those 600 bytes then snort detects that time with my developed rule. But If I 
generate a malformed PDF File through MSF then the malformed objects are being moved to > 600 and the pattern is 
present at last of the PDF file (around at 20000th offset). In such cases snort is not detecting the attack. I 
checked the signature and everything is perfect as I haven't given any such offset limitations inside that rule.

    I gave a look in snort.conf to see the http_preprocessor configs and the checked till how far snort processes the 
data length and it is set to 0. So I think it should work in any case.

Can anyone please guide me on what could be the issue and how I can resolve this?


Best Regards,Sujit


-- 
Joel Esler

------------------------------------------------------------------------------
What happens now with your Lotus Notes apps - do you make another costly 
upgrade, or settle for being marooned without product support? Time to move
off Lotus Notes and onto the cloud with Force.com, apps are easier to build,
use, and manage than apps on traditional platforms. Sign up for the Lotus 
Notes Migration Kit to learn more. http://p.sf.net/sfu/salesforce-d2d
_______________________________________________
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:

Snort doesn't trigger while the payload size is big (even for ~4-5KB files) Sujit Ghosal (Dec 04)
- Re: Snort doesn't trigger while the payload size is big (even for ~4-5KB files) Joel Esler (Dec 05)
  - Re: Snort doesn't trigger while the payload size is big (even for ~4-5KB files) Sujit Ghosal (Dec 13)
    - Re: Snort doesn't trigger while the payload size is big (even for ~4-5KB files) Joel Esler (Dec 13)
    - Re: Snort doesn't trigger while the payload size is big (even for ~4-5KB files) Sujit Ghosal (Dec 13)
    - Re: Snort doesn't trigger while the payload size is big (even for ~4-5KB files) Joel Esler (Dec 13)
    - Re: Snort doesn't trigger while the payload size is big (even for ~4-5KB files) Sujit Ghosal (Dec 14)