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Snort doesn't trigger while the payload size is big (even for ~4-5KB files)
From: Sujit Ghosal <thesujit () gmail com>
Date: Sun, 5 Dec 2010 12:23:08 +0530

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
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