Cutwail/PushDo SMTP Attack Vulnerability Detection

ReubenFarrelly — Sun, 01 Nov 2015 00:23:39 GMT

I've recently set up a new PA-100-VM and been closely analysing it along with all of the traffic that goes through it. It is running 7.0.3 along with the latest updates to all definition files (updated nightly).

In the process of doing this I've determined that the PA is not picking up on a fairly common SMTP attack - that being the Cutwail SMTP auth brute force. There is a bit more info about this here:

https://blog.avast.com/2013/06/25/15507/

https://serverfault.com/questions/667322/email-server-attack-from-telnet

A machine infected with this worm will attempt to brute force SMTP auth other random machines on the Internet.

The good thing is that all of the attempts involve a very characteristic SMTP EHLO of ylmf-pc. So they are patently obvious to identify.

I've written a custom malware signature that detects this and IP blocks the offending hosts for the maximum 3600s (I would block for longer if this was possible). This works well. Lots of hits and no brute forcing anymore 😉

The questions I have are:

- Is there a way to submit this to Palo Alto so that this attack is picked up by the threat signatures without me having to write a custom vulnerability sig? I can open a case but I would have thought there were easier ways than this to have this information fed into the system.

- Is there a reason this hasn't been already added? This is a very common vulnerability by all accounts. I haven't tried but I imagine the PA will pick up on the trojan exe's that this worm uses to transmit itself, but as a non-infected user I also want protection from other remote machines who have been exploited and I would expect the appliance would be protecting me from known brute force attacks.

Re: Cutwail/PushDo SMTP Attack Vulnerability Detection

pulukas — Sun, 01 Nov 2015 11:54:03 GMT

The best way to communicate on these types of issues with Palo Alto is by opening an official support ticket.

Support will first be able to determine what current signatures are aimed at this vulnerabiliity. This will be fastest if you have the CVE handy.

Assuming there is an approach against the CVE, they will be able to determine if you are correctly configured so that the traffic is reviewed against the existing signature.

Should there not be anything in place now, they can also be your conduit to submit requests for enhancements to the correct team.

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Cutwail/PushDo SMTP Attack Vulnerability Detection

Re: Cutwail/PushDo SMTP Attack Vulnerability Detection