EXECryptor226DLLminimumprotection

Hunt Hypothesis

This rule identifies the presence of the EXECryptor226 DLL, a component often associated with the EXECryptor malware family, which adversaries may deploy to establish persistence or execute malicious payloads within Azure environments. Proactively hunting for this artifact allows the SOC team to detect low-severity implantations early, preventing potential lateral movement or privilege escalation before the threat matures into a more significant incident.

YARA Rule

rule EXECryptor226DLLminimumprotection
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 8B C6 87 04 24 68 [4] 5E E9 [4] 85 C8 E9 [4] 81 C3 [4] 0F 81 [3] 00 81 FA [4] 33 D0 E9 [3] 00 0F 8D [3] 00 81 D5 [4] F7 D1 0B 15 [4] C1 C2 ?? 81 C2 [4] 9D E9 [4] C1 E2 ?? C1 E8 ?? 81 EA [4] 13 DA 81 E9 [4] 87 04 24 8B C8 E9 [4] 55 8B EC 83 C4 F8 89 45 FC 8B 45 FC 89 45 F8 8B 45 08 E9 [4] 8B 45 E0 C6 00 00 FF 45 E4 E9 [4] FF 45 E4 E9 [3] 00 F7 D3 0F 81 [4] E9 [4] 87 34 24 5E 8B 45 F4 E8 [3] 00 8B 45 F4 8B E5 5D C3 E9 }

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

• Scenario: An IT administrator manually runs a custom PowerShell script to encrypt sensitive configuration files using AES-CBC with a 256-bit key before archiving them to a secure share. The script explicitly sets the encryption mode to CBC and uses a key size that matches the rule’s threshold, triggering the alert despite being a standard manual backup procedure.

  • Filter/Exclusion: Exclude processes where the parent process is powershell.exe or pwsh.exe and the command line contains specific keywords like -Encrypt or Set-ItemProperty targeting known backup paths (e.g., \\fileserver\backups\config).

• Scenario: A CI/CD pipeline agent (e.g., Jenkins or Azure DevOps) executes a build step that uses openssl enc to encrypt intermediate artifacts with AES-256-CBC for transfer between build agents. The detection rule flags the openssl process because it uses a “minimum protection” cipher suite (CBC) rather than GCM, even though the context is an internal, trusted network segment.

  • Filter/Exclusion: Exclude processes named openssl.exe or openssl where the parent process is a known CI/CD agent (e.g., jenkins-agent.exe, vstsagent.exe) and the working directory resides within the build workspace path (e.g., C:\Jenkins\workspace\ or /home/vstsagent/).

• Scenario: A database administrator performs a nightly maintenance task using pg_dump followed by gpg (GnuPG) to encrypt the SQL dump file. The underlying encryption algorithm used by GPG defaults to a symmetric cipher that may be interpreted by the rule as a “minimum protection” standard if the rule inspects the raw cipher suite metadata, leading to a false positive during routine DB backups.

  • **Filter/