Guesswho Ransomware actively spreading in the wild

July 12, 2019

The SonicWall Capture Labs Threat Research Team observed reports of a new variant family of Guesswho ransomware [Guesswho.RSM] actively spreading in the wild.

The GUESSWHO ransomware encrypts the victim’s files with a strong encryption algorithm until the victim pays a fee to get them back.

Infection Cycle:

The ransomware adds the following files to the system:

  • Malware.exe
    • %Userprofile\Desktop %\ How Recovery Files.txt
      • Instruction for recovery
    • %App.path%\ [Random]. GUESSWHO
    • %Userprofile\Desktop %\ How Recovery Files.txt

Once the computer is compromised, the ransomware runs the following commands:

 

The ransomware encrypts all the files and appends the [.GUESSWHO]  extension onto each encrypted file’s filename.

After encrypting all personal documents, the ransomware shows the following text file containing a message reporting that the computer has been encrypted and to contact its developer for unlock instructions.

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

 

 

SonicWall Capture Labs provides protection against this threat via the following signature:

  • GAV: Guesswho.RSM (Trojan)

This threat is also detected by SonicWALL Capture ATP w/RTDMI and the Capture Client endpoint solutions.