ExeShieldCryptor13RCTomCommander

Hunt Hypothesis

This detection identifies the execution of a specific cryptographically signed or obfuscated executable associated with the ExeShieldCryptor13RCTomCommander family, which often indicates initial access or fileless malware activity within the environment. Proactively hunting for this signature in Azure Sentinel allows the SOC team to validate legitimate business processes against potential stealthy threats that may evade standard heuristic-based detections due to their low severity classification and specialized YARA pattern matching.

YARA Rule

rule ExeShieldCryptor13RCTomCommander
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 53 56 57 60 E8 00 00 00 00 5D 81 ED 8C 21 40 00 B9 51 2D 40 00 81 E9 E6 21 40 00 8B D5 81 C2 E6 21 40 00 8D 3A 8B F7 33 C0 EB 04 90 EB 01 C2 AC }

condition:
		$a0 at pe.entry_point
}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the ExeShieldCryptor13RCTomCommander detection rule, along with suggested filters and exclusions:

• Scenario: Automated Backup Encryption by Veeam or Commvault

  • Context: Enterprise backup agents (e.g., Veeam.Backup.Service.exe or commvault.cmd) frequently scan and encrypt large volumes of data on the file system. The YARA rule may misinterpret these legitimate encryption operations as the behavior of the ExeShield cryptor, especially when processing .exe or document files in shared network drives.
  • Filter/Exclusion: Create a whitelist exclusion based on the process image path and parent process name.
    • Condition: Process.ImagePath contains "C:\Program Files\Veeam\Backup & Replication" OR Process.ParentImageName == "Veeam.Backup.Service.exe".

• Scenario: Scheduled Antivirus Definition Updates (Microsoft Defender)

  • Context: During off-hours, Microsoft Defender runs scheduled scans and updates its definition database. The update engine often executes a command-line tool to unpack and encrypt new signature files, which matches the specific byte patterns or string signatures defined in the ExeShieldCryptor13RCTomCommander rule.
  • Filter/Exclusion: Exclude processes running under the context of the Windows Update service or Defender Service.
    • Condition: Process.ImagePath contains "C:\ProgramData\Microsoft\Windows Defender" AND Process.CommandLine contains "mpcmdrun.exe".

• Scenario: Deployment of Application Patches via SCCM/MECM

  • Context: System Center Configuration Manager (SCCM) or Microsoft Endpoint Configuration Manager often deploys application updates that involve repackaging executables. The deployment agent (ccmexec.exe) may