EPv10

Hunt Hypothesis

This rule detects potential malicious or obfuscated executables by analyzing specific entry point characteristics, indicating an adversary may be deploying custom or packed payloads to evade standard signature-based detection. Proactively hunting for these indicators in Azure Sentinel allows the SOC team to identify low-severity anomalies that could serve as initial access vectors or persistence mechanisms before they escalate into more significant compromises.

YARA Rule

rule EPv10
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 83 C0 17 8B F0 97 33 C0 33 C9 B1 24 AC 86 C4 AC AA 86 C4 AA E2 F6 00 B8 40 00 03 00 3C 40 D2 33 8B 66 14 50 70 8B 8D 34 02 44 8B 18 10 48 70 03 BA 0C [4] C0 33 FE 8B 30 AC 30 D0 C1 F0 10 C2 D0 30 F0 30 C2 C1 AA 10 42 42 CA C1 E2 04 5F E9 5E B1 }

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

• Antivirus/EDR Engine Updates: Legitimate security agents like CrowdStrike Falcon, Microsoft Defender for Endpoint, or Trellix frequently update their heuristic engines or drop new signature files. These updates often involve writing new PE (Portable Executable) binaries to disk or modifying existing ones, which can trigger YARA rules looking for specific entry point anomalies or version strings.
  • Filter: Exclude processes originating from the security agent’s install directory (e.g., C:\Program Files\CrowdStrike\, C:\Program Files\Microsoft Security Client\) or filter by known parent process names (FalconSensor.exe, MsMpEng.exe).
• Software Patching via Group Policy or WSUS: When Windows Update or enterprise patch management tools like Ivanti or SCCM apply cumulative updates, they often replace system DLLs or executables. The “new” file written during the patching process may have a slightly different entry point structure or version metadata that matches the YARA pattern, especially if the rule targets specific compiler artifacts or version numbers.
  • Filter: Exclude events where the parent process is TrustedInstaller.exe or wuaexer.exe, or filter out file paths containing \Windows\Installer\ or \SoftwareDistribution\.
• Development Build Artifacts in CI/CD Pipelines: In enterprise DevOps environments, Jenkins, Azure DevOps, or GitHub Actions agents compile and build applications. The resulting binaries are often written to temporary build directories. If the YARA rule is sensitive to debug symbols, specific compiler banners, or unstripped entry points, these freshly built, unoptimized executables will frequently match.
  • Filter: Exclude file paths containing \builds\, \workspace\, or \artifacts\, or filter by parent processes associated with CI/