While reviewing recent reports scanned by ZULU, we came across a malicious report that drew our attention. It was notable as the final redirection downloaded ZIP content by accessing a PHP file on the domain 'www.stisanic.com'.
The ZULU report turned out be live example of Backdoor Xtrat, which is a relatively old threat but one that many AV vendors are still not consistently detecting. AV vendors had first released a signature for this malware in May 2011 (MS advisory). The poor AV detection is the result of a common challenge - the attackers consistently alter the binary and there are numerous variants. This is of course a known limitation of signature based approaches and something that attackers regularly take advantage of. It's also a reason why security vendors, like Zscaler, are increasingly relying on behavioral analysis when analyzing binary files. Behavioral analysis doesn't rely on signatures or require any prior knowledge of the threat and is a key component in the Cloud-based APT solution that Zscaler released in 2013.
Zscaler behavioral analysis report:
Screen capture of the Zscaler Behavioral Analysis report for Backdoor.Xtrat
Typical behavior of this backdoor:
Injects itself into svchost.exe, exploere.exe and iexplore.exe
Drops PE files
Performs network activity to accept commands from a remote server and sends data to the remote server
Dropped file details:
The backdoor drops the following two EXE files on victim's machine. Both of the EXE files are same, but are dropped with different names.