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RE: nikto, n-stealth can crash the web-server?
From: "Evans, Arian" <Arian.Evans () fishnetsecurity com>
Date: Fri, 14 Jul 2006 16:04:16 -0500


-----Original Message-----
From: Matthias Heinrich [mailto:matze-heinrich () gmx de] 
I'm trying to find out if web-scanners like n-stealth or 
nikto can crash the web-server and why.

I've seen nikto in particular cause crashes, and Nessus
plugins, but it always depends on the webserver & the
check, and usually it's not too hard to hunt down.


+ Chunked encoding tests on older IIS & apache versions

+ There's a Cisco ACS BoF check through a long URL string
that I've seen crash custom webservers due to the character
sets used to create the URL payload, or the size, not being
handled properly.

+  Threads: on custom web servers, poorly coded threading
can thread-lock the thing.

+ Sockets: I ran into Tomcat implemented with some custom
sockets programming that choked on multi-threaded tests
due to inability to close & recycle TCP connections fast
enough (would simply run out of proc, then mem).

+ TCP/IP stack: this is mostly old news, but I've seen
www and db servers fail due to the stack crashing on
several OSes, like old HPUX, and OpenVMS stuff back when
you had vendor-supplied custom stacks, and same with
some older Unisys systems that they customized the IP stack.

You couldn't even port-scan some of those old systems
w/out them crashing; see Sockets: above.

Then there is simply resource exhaustion, possibly due
to system limitations or web server misconfiguration.

Hope that gives you some ideas,

Arian J. Evans
FishNet Security
913.710.7085 [mobile]
816.701.2045 [office]


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