Multi-Level-Encoding BLOCKING

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Multi-Level-Encoding BLOCKING

L1 Bithead

Can anyone report successfully passing these tests?:

And what combination of settings did it?

Default Multi-Level-Encoding BLOCKING doesnt seem to catch what is doing.



L7 Applicator

I had a chance to look at this a little bit.  I disagree with their pass/fail criteria.  According to them, in order to pass their test, your firewall must accept the entire file, iteratively decompress, and block based on detecting the eicar file.  


When you block multi-level encoded files, PAN-OS stops the 5x-10x ZIP files from being transferred in the first place.  (Un)Fortunately, PAN-OS stops the transfer of these files before it gets to the eicar virus.  Fortinet calls this a "fail" because it wasn't blocked based on their "AntiVirus" detection criteria.  Personally, I'd call it a success.... why would I want to allow something that's been zipped more than 5 times into my network?  No thank you.  I think PAN-OS should get extra credit for stopping the malicious file earlier on in the download process.


Similar things can be said for the rest of the file types.  I'm trying to remember the last time I downloaded a tar, tar.gz, rar, 7z, passworded zip, or ARJ file on my desktop.  Well, I do remember ARJ at least... it was about 1998.  Each environment is different, but my file blocking profiles prevent the transfer of these riskier file types (along with quite a few others) unless they come through approved applications ie: CABs through ms-update only from, or tar.gz from an approved repository for my linux servers.  


TL;DR is that when I ran the test, the eicar virus file never entered my network.  Fortinet didn't like how it was done so they gave me a 5/18 score.  The eicar file never entered my network, so I gave myself 18/18 and patted myself on the back.

Half the archives I work with are tgz. I think your attempt to discredit the test based on your usage is pretty naive. I agree with your first comment though about blocking based on levels of containers. However, products like Sophos seem to be able to inspect arbitrary levels, it is frustrating that PA have chosen a specific limit.

sophos only has to focus on one thing, and speed is not a big issue. At the firewall level, speed while maintaining accuracy is paramount thus parallel processing is required. this also means a session can be rejected based on the first negative hit, rather than tallying hits for every single stage. (this means more effcient use of resources)


the deeper inside an archive a system needs to go, the more resources are consumed and for a system sitting at the perimeter, resources are precious: starting from PAN-OS 7.0, the 'depth' of decoding has been increased to 4 levels, which should be more than sufficient for any normal archive.

Tom Piens
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