Never say never

There was a time when image files, such as JPEGs, were considered harmless. Some industry pioneers stated outright that only executable (EXE, COM) files could carry viruses. And then came macro viruses, spreading from .DOC files, another “impossible” propagation vector. And later, some said that you couldn’t really get a virus from just reading an email – you had to click on an attachment. Of course, this has been proved false, thanks to an (almost) unending stream of Outlook vulnerabilities.

The misconception that JPEGS can’t carry viruses was disproved by a major vulnerability discovered last year in a graphics format parsing library used in many products. Several Trojans exist which attempt to make use of this vulnerability to infect computers. We’ve added a generic detection for malicious JPEG files of this type: Exploit.Win32.MS04-028.gen.

This weekend we intercepted an interesting attempt at spreading a Trojan using the above mentioned JPEG exploit. Somebody mass mailed a large number of messages containing a downloader for Backdoor.Win32.Haxdoor.dw. The downloader,a malcrafted JPEG exploit 4098 bytes in size (md5: 09617ea4db6de83455ed4079facdbc36) doesn’t work.

As often happens with virus writers, he/she probably didn’t bother to test the exploit before sending it out, and as a result, the exploit which has been widely distributed doesn’t work. So this time at least, the JPEG file wasn’t infectious. However, fixing the mistake would be relatively easy and we wouldn’t be surprised to see a second wave, this time with a working exploit.