Trojan-Dropper:OSX/Revir.C

Unlike previous variants in the Revir malware family, Trojan-Dropper:OSX/Revir.C is distributed as an application bundle, comprised of the following components:

• The main binary - detected as Trojan-Dropper:OSX/Revir.C
• .conft - Contains an encrypted payload
• .confr - contains a decoy JPG file. The first 2048 bytes are also used as the RC4 key to decrypt the payload
• .cnf - contains the filename to be used when creating the decoy file

Payload

On execution, the malware drops and executes its payload as the following:

• /tmp/.mdworker

In the samples analyzed, the payload contained another malware detected as Backdoor:OSX/Imuler.A; however, since Revir.C is an application bundle, other malware may be used in other samples.

Social Engineering

During execution, the Revir.C sample analyzed displayed a sexy image of Russian model Irina Shayk, apparently taken from the March 2012 issue of FHM (South Africa) magazine, as a decoy to distract the user from the program's more malicious activities.

To do this, Revir.C drops a copy of the decoy file to the /tmp folder and opens it using the 'open' command. This command directs OS X to use the default application handling the target file's filetype for this action; this means that unlike previous Revir variants, the decoy file is not limited to PDF or JPG.

As further insurance, Revir.C also drops another copy of the decoy file in the folder where the malware was executed, then deletes itself; presumably this is done so that if the user attempts to find the application they just executed, they would only find the decoy file instead.

Both copies of the decoy file uses the filename specified in the .cnf component. If the .cnf compoenent does not exist, the decoy files use the default filename "TMP0M34JDF8".