EXECryptor226minimumprotection

Hunt Hypothesis

This detection identifies potential file encryption activities characteristic of ransomware or data exfiltration attempts by monitoring for specific executable behaviors defined in the EXECryptor226 YARA rule. Proactive hunting is essential to validate these low-severity signals early, ensuring that subtle encryption patterns are not overlooked before they escalate into critical incidents within the Azure Sentinel environment.

YARA Rule

rule EXECryptor226minimumprotection
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 68 [4] 58 81 E0 [4] E9 [3] 00 87 0C 24 59 E8 [3] 00 89 45 F8 E9 [4] 0F 83 [3] 00 E9 [4] 87 14 24 5A 57 68 [4] E9 [4] 58 81 C0 [4] 2B 05 [4] 81 C8 [4] 81 E0 [4] E9 [3] 00 C3 E9 [4] C3 BF [4] 81 CB [4] BA [4] 52 E9 [3] 00 E8 [3] 00 E9 [3] 00 E9 [4] 87 34 24 5E 66 8B 00 66 25 [2] E9 [4] 8B CD 87 0C 24 8B EC 51 89 EC 5D 8B 05 [4] 09 C0 E9 [4] 59 81 C1 [4] C1 C1 ?? 23 0D [4] 81 F9 [4] E9 [4] C3 E9 [3] 00 13 D0 0B F9 E9 [4] 51 E8 [4] 8B 64 24 08 31 C0 64 8F 05 00 00 00 00 5A E9 [4] 3C A4 0F 85 [3] 00 8B 45 FC 66 81 38 [2] 0F 84 05 00 00 00 E9 [4] 0F 84 [4] E9 [4] 87 3C 24 5F 31 DB 31 C9 31 D2 68 [4] E9 [4] 89 45 FC 33 C0 89 45 F4 83 7D FC 00 E9 [4] 53 52 8B D1 87 14 24 81 C0 [4] 0F 88 [4] 3B CB }

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 EXECryptor226minimumprotection detection rule, including suggested filters and exclusions:

• Antivirus Real-Time Scanning of Encrypted Archives

  • Scenario: The enterprise endpoint protection suite (e.g., Microsoft Defender Antivirus or Symantec Endpoint Protection) initiates a real-time scan on a large .zip or .7z archive containing encrypted binaries. The YARA rule detects the cryptographic signatures within the archive as potential “minimum protection” encryption activity, triggering an alert even though this is standard scanning behavior.
  • Filter/Exclusion: Exclude processes where ParentImageName matches the antivirus engine (e.g., MsMpEng.exe, Rtvscan64.exe) and the file extension is .zip, .7z, or .gz.

• Scheduled Backup Job Execution

  • Scenario: A nightly scheduled task runs a backup utility like Veeam Agent or Acronis Cyber Protect. During the job execution, the tool encrypts data blocks before writing them to the storage repository. The rule interprets these encryption operations as new executable protection events rather than routine maintenance.
  • Filter/Exclusion: Create an exclusion based on Scheduled Task Name containing keywords like “Backup”, “Veeam”, or “Acronis,” and filter by process name (e.g., vss.exe, acronis.backup.engine.exe) running during the defined maintenance window (e.g., 01:00–04:00 UTC).

• Software Deployment via Configuration Management Tools

  • Scenario: An IT administrator deploys a new application package using Microsoft Endpoint Configuration Manager (SCCM) or Ivanti Neurons. The deployment agent (ccmexec.exe or IvantiAgent.exe) extracts and encrypts