[Snort-sigs] http_header issues, Snort 2.8.5.3

Will Metcalf william.metcalf at ...2420...
Thu Apr 1 10:33:38 EDT 2010


That because the cookie isn't included in the normalized header
buffer, you can only get to via http_cookie modifer.  I know it
doesn't make any sense to me either.  I sent the following e-mail to
snort-devel on 3/17.

"This is just my 2 cents, but I don't think the following behavior
makes sense.  I think that even though you are providing http_cookie
as a separate buffer to match on it should still be included in the
http_header buffer, well because it is part of the headers.

You can still match using the raw buffer but then you have to add
additional checks to try and differentiate between the headers and the
body which is why I'm guessing these modifiers were created in the
first place.  I realize that in most cases header order doesn't matter
but there may be instances where you can fingerprint a piece of
automated code (read malware) using a rule similar to sid 69 below.

Regards,

Will"

#this matches but I loose the performance/accuracy benefit of only
matching within the buffer containing http_headers.
alert tcp any any -> any any (msg:"http_cookie + ";
content:"Cookie|3A|
e6504ae48c99f09df7f58996aacbb6b0=120e494ce857d6ceeef89f9678d4d703|0d
0a|Content-Type|3A| application"; classtype:bad-unknown; sid:68;
rev:1;)

#this fails to match as the cookie is not part of the http_header
buffer but is part of the real http headers.
alert tcp any any -> any any (msg:"http_cookie + ";
content:"Cookie|3A|
e6504ae48c99f09df7f58996aacbb6b0=120e494ce857d6ceeef89f9678d4d703|0d
0a|Content-Type|3A| application"; http_header; classtype:bad-unknown;
sid:69; rev:1;)



On Thu, Apr 1, 2010 at 9:22 AM, evilghost at ...3397...
<evilghost at ...3397...> wrote:
> Hello, I am running Snort 2.8.5.3 and it appears that either
> http_header; is not working correctly, does not work with a relative
> keyword, or I do not understand http_header; correctly.  I am attempting
> to constrain a content match to the http_header for performance reasons.
>
> Note, no need to recommend isdataat, I know there is data within 1024
> bytes past the previous content match.
>
> Does NOT work:
>    uricontent:"/login.php"; fast_pattern; content:"|0d 0a|Cookie\: ";
> nocase; http_header; content:"ieatbugs="; within:1024;
>
> Does work:
>    uricontent:"/login.php"; fast_pattern; content:"|0d 0a|Cookie\: ";
> nocase; content:"ieatbugs="; within:1024;
>
> Comments/insight appreciated.
>
> -evilghost
>
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