New Locky Ransomware Uses JScript files to avoid detection in the wild

July 28, 2016

The Dell Sonicwall Threats Research team observed reports of a new Spam wave of Locky Malware family named GAV: JScript.Nemucod.AY and JScript.Grabber.KM actively spreading in the wild.

This recently discovered variant of the Locky uses Encrypted JScript files to avoid detection.

The malware spreads via spam waves and since the malware comes with a simple Jscript file its seems legitimate and trustworthy at first glance.

Infection Cycle:

The Malware uses the following icons:

The Malware adds the following files to the system:

  • detailed analysis.wsf

    • %Userprofile%Local SettingsTempXobkg60rnv.exe

  • Sales report.wsf

    • %Userprofile%Local SettingsTempmSsruTKAbsXRp.exe

The Malware comes in two different versions, one acts as downloader and the other act as dropper.

Here is an example of downloader version:

As you can see the malware uses some Jscript technique to evade detections by firewalls.

Here is the dropper example witch comes with an embedded executable file.

Once the computer is compromised, the malware copies its own executable file to %Userprofile%Local Settings Temp folder.

The Malware encrypts the victims files with a strong RSA 2048 encryption algorithm until the victim pays a fee to get them back.

After encrypting all the personal documents and files it shows the following web page:

It demanded victims pay the equivalent of Money in Bitcoin virtual currency in order to receive the decryption key that allows them to recover their files.

Command and Control (C&C) Traffic

The Malware performs C&C communication over 80 ports. The malware sends your system information to its own C&C server via following format, here are some examples:

We have been monitoring varying hits over the past few days for the signature that blocks this threat:

SonicWALL Gateway AntiVirus provides protection against this threat via the following signatures:

  • GAV: JScript.Nemucod.AY (Trojan)

  • GAV: JScript.Grabber.KM (Trojan)