full-disclosure - Re: Qualys scanner detects rst.b trojan?

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From: smanley at qualys.com (Scott Manley)
Subject: Re: Qualys scanner detects rst.b trojan?

ned wrote:
> Hi
> 
> I recently had an infection on one of my machines with the linux rst.b trojan. 
> Qualys has a more or less detailed analysis of the code, and provides a 
> remote detection tool here. 
> https://www.qualys.com/forms/remoteshellb.html
> But even though I saw the running trojan process, knew the port of it and it 
> was listening for incoming connections, Qualys' remote detection tool told me 
> my host was clean. Did anyone run over the same behaviour? Is there a working 
> remote detection utility?  

Ned - thanks for the infected binaries.
What you have here is 2 different linux viruses, neither of them appears 
to be a vanilla rst.b

One is the OSF virus, it is a 8192 byte package which attaches to ELF 
files in a similar manner to RST, on execution it forks and tries to 
debug itself - and exits if it can't. It then tries to infect up to 200 
files in the local directory and in /bin, before launching a backdoor on 
port 29369. It doesn't do any of the raw socket stealth communication 
that RST uses, so the remote detection method we use in the code  does 
not flag this as the RST.B trojan. However, a signature has been 
developed for the Qualysguard scanner and will be released soon.

The local detection tools still detect the infection since they operate 
based upon detecting the changes to the ELF structure which the viruses 
perform during the infection process.

The second file also gets flagged as an RST virus, however I've not 
managed to observe it doing anything else other than infecting a few 
test files. I don't see any raw sockets or otherwise, we'll look a 
little harder, our test setup may not be RST friendly, we'll look at a 
few other avenues. But it appears that there is nothign to detect - 
again this would explain why the tools can't detect a backdoor, because 
it doesn't exist.

Scott Manley
Vulnerability Engineer
Qualys Inc.