Re: Possible IDS-evasion technique

From: Sullo sq (sqat_private)
Date: Fri Feb 15 2002 - 15:05:14 PST

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    0.9 was (is?) a valid HTTP version, so that is why Netscape/Apache (and most others) are answering the request properly.  An IDS _should_ not care the HTTP version for a signature matching text on 'phf'.  (of course, I suspect encoding /cgi-bin/phf string would also fool the IDS in this case...).
    
    Sullo
    
    > I've accidently found a way to bypass IDS detection for HTTP
    > requests. I've seen this behaviour on some older version of 
    > IIS RealSecure network IDS and I wonder if this works on any 
    > other IDSes.
    [snip]
    > Request:
    > GET /cgi-bin/phf HTTP/0.9
    > Connection not reset, HTTP server replies "file not found"
    > 
    > Apparently the last form of request allows to get a meaningful
    > reply from HTTP server while IDS does not mind it.
    > 
    > Apache and Netscape Entriprise will happily reply to the last
    > form of request, didn't try it on other web servers.
    > 
    > Alla.
    > 
    > 
    
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