Detects REvil Linux - Revix 1.1 and 1.2

Hunt Hypothesis

This hunt targets adversaries deploying the REvil Linux variant (Revix) to establish persistence on critical workloads within Azure Sentinel. Proactively hunting for these specific indicators is essential because early detection of this low-severity activity can prevent lateral movement and data exfiltration before the ransomware payload executes.

YARA Rule

rule Revil_Ransomware : ransomware {
   meta:
      author = "Josh Lemon"
      description = "Detects REvil Linux - Revix 1.1 and 1.2"
      reference = "https://angle.ankura.com/post/102hcny/revix-linux-ransomware"
      date = "2021-11-04"
      version = "1.1"
      hash1 = "f864922f947a6bb7d894245b53795b54b9378c0f7633c521240488e86f60c2c5"
      hash2 = "559e9c0a2ef6898fabaf0a5fb10ac4a0f8d721edde4758351910200fe16b5fa7"
      hash3 = "ea1872b2835128e3cb49a0bc27e4727ca33c4e6eba1e80422db19b505f965bc4"
   strings:
      $s1 = "Usage example: elf.exe --path /vmfs/ --threads 5" fullword ascii 
      $s2 = "uname -a && echo \" | \" && hostname" fullword ascii
      $s3 = "esxcli --formatter=csv --format-param=fields==\"WorldID,DisplayName\" vm process list" ascii
      $s4 = "awk -F \"\\\"*,\\\"*\" '{system(\"esxcli" ascii
      $s5 = "--silent (-s) use for not stoping VMs mode" fullword ascii
      $s6 = "!!!BY DEFAULT THIS SOFTWARE USES 50 THREADS!!!" fullword ascii
      $s7 = "%d:%d: Comment not allowed here" fullword ascii
      $s8 = "Error decoding user_id %d " fullword ascii 
      $s9 = "Error read urandm line %d!" fullword ascii
      $s10 = "%d:%d: Unexpected `%c` in comment opening sequence" fullword ascii
      $s11 = "%d:%d: Unexpected EOF in block comment" fullword ascii
      $s12 = "Using silent mode, if you on esxi - stop VMs manualy" fullword ascii
      $s13 = "rand: try to read %hu but get %lu bytes" fullword ascii
      $s14 = "Revix" fullword ascii
      $s15 = "without --path encrypts current dir" fullword ascii
      
      $e1 = "[%s] already encrypted" fullword ascii
      $e2 = "File [%s] was encrypted" fullword ascii
      $e3 = "File [%s] was NOT encrypted" fullword ascii
      $e4 = "Encrypting [%s]" fullword ascii

   condition:
      uint16(0) == 0x457f and filesize < 300KB and ( 4 of ($s*) and 2 of ($e*))
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 19 string patterns in its detection logic.

References

• https://angle.ankura.com/post/102hcny/revix-linux-ransomware
• Source Rule

False Positive Guidance

Here are specific false positive scenarios for the Detects REvil Linux - Revix 1.1 and 1.2 rule in an enterprise environment, along with suggested filters:

• Automated Backup Executions via Veeam or Commvault

  • Scenario: Enterprise backup agents (e.g., Veeam Agent for Linux or Commvault Simpana) frequently spawn child processes to compress and encrypt data blocks. These operations often involve rapid file creation, modification of binary archives, and the use of standard compression libraries that mimic the behavior patterns of the Revix ransomware encryption phase.
  • Filter/Exclusion: Exclude process paths containing /opt/veeam, /usr/bin/vbragent, or /commvault from the alert logic. Additionally, filter out events where the parent process is vbrservice or siman.exe.

• System Patching and Configuration Management (Ansible/Satellite)

  • Scenario: During scheduled maintenance windows, configuration management tools like Red Hat Satellite or Ansible execute playbooks that update system libraries (glibc, openssl) and modify critical configuration files. The mass file writes and permission changes triggered by these automation scripts can generate the same hash-based anomalies detected as Revix activity.
  • Filter/Exclusion: Create an exclusion for processes running under specific service accounts (e.g., ansible-runner, rhsmcertd) or command lines containing keywords like -p playbook.yml and --check. Schedule these exclusations to apply specifically during known maintenance windows (e.g., Sundays 02:00–04:00 UTC).

• Container Orchestration Image Scanning (Trivy/Clair)

  • Scenario: In containerized environments, security scanners like Trivy or Clair run periodically to analyze Docker images. These tools extract layers and scan binary