W32/Cypher.F308!tr.ransom is a detection for a Ransomware Cipher trojan.
Below are some of its observed characteristics/behaviours:

  • This malware may drop any of the following file(s):
    • HOW_TO_DECRYPT_FILES.html : This html file is dropped in every infected folder and will serve as ransom note.
    • %AppData%\[Random2].exe : This file is the copy of the original malware itself.
    • %AppData%\encryption_key : This file contains a set of encryption keys for the infected system.

  • Affected files of this Ransomware may use one of the following filenaming formats:
    • {OriginalFilename.Ext}.cypher
    • {OriginalFilename.Ext}.xcry7684

  • This malware was also observed to affect/encrypt files located on shared drive within the same subnet.

  • This malware was also observed to affect/encrypt files located on USB or external drives.

  • Affected victims of this Ransomware are redirected by the attacker via:

  • This malware may apply any of the following registry modification(s):
    • HKEY_CURRENT_USER\Software\Microsoft\Windows\Currentversion\Run
      • [Random1] = %AppData%\[Random2].exe
      The malware configures itself to run every time the infected user logs on.

  • Below is an illustration of the malware's Ransom notes:

    • Figure 1: Ransom note.

    • Figure 2: Encryption key file.

Recommended Action

  • Make sure that your FortiGate/FortiClient system is using the latest AV database.
  • Quarantine/delete files that are detected and replace infected files with clean backup copies.