Irregular Expressions

Nov 4 2010   11:46PM GMT

SonicWall IPS evasion

Dan O'Connor Dan O'Connor Profile: Dan O'Connor

Well this did work a few weeks ago.

Until a week or so ago, someone could use an IPS evasion module in Metasploit to pass attacks through a SonicWall.  This involved using DCE / RPC Fragmentation which fragments the packets during the NetBIOS session setup.

This has been known since at least 2006 ish when Snort implemented a dynamic pre-processor to handle this in it’s engine.  Several other UTM’s have the ability to detect this type of traffic, most of them based on the Snort pre-processor.

Last week I was successfully getting the ms10_061 passed the SonicWalls IPS engine and AV engine using the fragmentation.  I did not specifically chose the ms10_061, but it was in the list of top 10 blocked attacks on the dashboard.


It worked.

Turn off the Frag,



Right through like Jim Morrison.

I reported the issue to SonicWall and after a some debate there is a new signature.

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