Daily Archives: 2007-09-07

Analysis of the Storm Javascript exploits

On Monday I formally joined the Tor project and it certainly has been an interesting week. Yesterday, on both the Tor internal and public mailing lists, we received several reports of spam emails advertising Tor. Of course, this wasn’t anything to do with the Tor project and the included link was to an IP address (it varied across emails). On visiting this webpage (below), the user was invited to download tor.exe which was not Tor, but instead a trojan which if run would recruit a computer into the Storm (aka Peacomm and Nuwar) botnet, now believed to be the worlds largest supercomputer.

Spoofed Tor download site

Ben Laurie, amongst others, has pointed out that this attack shows that Tor must have a good reputation for it to be considered worthwhile to impersonate. So while dealing with this incident has been tedious, it could be considered a milestone in Tor’s progress. It has also generated some publicity on a few blogs. Tor has long promoted procedures for verifying the authenticity of downloads, and this attack justifies the need for such diligence.

One good piece of advice, often mentioned in relation to the Storm botnet, is that recipients of spam email should not click on the link. This is because there is malicious Javascript embedded in the webpage, intended to exploit web-browser vulnerabilities to install the trojan without the user even having to click on the download link. What I did not find much discussion of is how the exploit code actually worked.

Notably, the malware distribution site will send you different Javascript depending on the user-agent string sent by the browser. Some get Javascript tailored for vulnerabilities in that browser/OS combination while the rest just get the plain social-engineering text with a link to the trojan. I took a selection of popular user-agent strings, and investigated what I got back on sending them to one of the malware sites.

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