Malware Evades Detection by counting amount of documents in recent files

A typical test environment consists of a fresh Windows computer image loaded into a VM environment. The OS image usually lacks documents and other telltale signs of real world use, Fenton said. The malware sample that Fenton found inside of a Word document looks for existing documents on targeted PCs.

If no Microsoft Word documents are found, the VBA macro code execution terminates, shielding the malware from automated analysis and detection. Alternately, if more than two Word documents are found on the targeted system, the macro will download and install the malware payload.
When documents are detected via RecentFiles, the malware assumes the system is a valid target and goes into action triggering a PowerShell script that links the victim’s PC to a command-and-control server to download a low-level system keylogger.

In another obfuscation technique, the malware uses an IP detection web service (Maxmind) to determine the network used by the targeted system. The IP address is cross referenced with a list of blacklisted IP addresses tied to security firms such as BlueCoat, Palo Alto and others. Those IPs are red flagged and stop the malware from executing, according to Fenton.

Source: Malware Evades Detection with Novel Technique | Threatpost | The first stop for security news

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