Wednesday, June 20, 2007

Malware Season Pt. 2

When we last left our heroes, they had de-obfuscated some JavaScript and downloaded a malware binary file named 'bin.exe'.

As you might have guessed, this binary was packed in order to make detecting its contents more difficult. I ran it through PEiD to determine what packer was used:

At this point, I don't even bother trying to unpack it. Instead, I try to load it in the GenOEP and ScanEP PEiD plugins and then I try to open it in OllyDbg. They all fail. Now I start to fear that I'm doomed to repeat past frustrations. But, what the hell, I'll try and unpack it anyway:

That was lucky. It can't be this easy. You may have noticed that the file in that screen shot is svhost32.exe, not bin.exe. This is because I was playing with it, trying to get it to run in SysAnalyzer. Since the VBScript dropper saves the file as svhost32.exe, I thought that might be worth a try. Anyway, to make sure there aren't more layers of packing going on here, I take another whack at it with PEiD:

I didn't see that coming, but I'm not looking a gift horse in the mouth. So now we should be able to do stuff like launch it in SysAnalyzer or OllyDbg. Sure enough, it runs from SysAnalyzer and we get the goodies:

Once it's running with SysAnalyzer, we can get the scoop. It uses AutoItv3 to download itself again as svhost.exe, modifies a mess of registry keys to run at start up as well as hijack Explorer and IE startup pages, presumably to drive up ad hits for the distributor.

A quick Google search, and we have a name for it: Sohanad. So it's not new malware, really, just slightly modified from the original so as to get by more AV scanners. I wonder how many:

The packed executable that we downloaded is detected by 13/31 AV products used by VirusTotal. Just for kicks, what happens if we try the unpacked file from earlier:

Ugh. Only 5/31 detect it now, when it's not obfuscated. The irony is overwhelming. Quick, somebody in the AV R&D field write a paper on using un-obfuscated code as a means of bypassing AV detection. This is hot!

Lastly, I contacted McAfee for an EXTRA.DAT file for both the packed and unpacked binaries and notified SANS ISC of the hacked web site with the dropper as well as the site hosting the binary.

I'd like to say, if you do run into sites hosting malware, the handlers at ISC are a great resource for coordinating response and clean-up. In this case, the hacked site was cleaned up and the malicious site was taken down within a day of my contacting ISC. They contacted the responsible parties and got it done. Doing this by yourself is hard and annoying work, and I am grateful to the ISC folks that they're willing to let us offload this stuff to them. So when you're out and about at conferences this summer and you see any of the ISC handlers, remember to thank them and maybe buy them a beer or something.

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