It seemed strange when the steady stream of changing, but similar, Mebroot (also known as Sinowal) executables dried up in late July. But alas, the mbr infecting family seems to have simply run out of flour and wheat for their “pasta theory” code, as described by Elia Florio and Kimmo Kasslin.
The spaghetti code typical of the Mebroot family for so long seems to have been straightened out. Known for downloading banking and financial service password stealers, it also developed a reputation for oodles of obfuscation in its executables. Now, instead of the neverending jmps, rets and scrambled code flow, the family seems to be released without the pasta and with a series of bogus calls — some DeviceIoControl with a stack full of NULL parameters, some bogus filenames passed to CreateFile, etc. Otherwise, the components observed in the lab match up with past Mebroot components, so we are digging deeper into the chances that we really are witnessing a new generation of the malware.
At the time we started digging into the dropper, googling “dedkeopght.com”, the site from which the malcrafted pdf file fetched this Mbr injecting payload, turned up no results whatsoever. Neither did scanning the payload file (the dropper) with a variety of AV file scanners. However, ThreatFire users are safe, and TF continues to prevent its injections and Mbr infection techniques.
Be sure to regularly update your software and add a behavioral solution to your system.