PEncrypt10JunkCode

Hunt Hypothesis

This detection identifies potential encryption-related junk code execution that may indicate early-stage ransomware activity or obfuscation attempts within the environment. A proactive hunt is essential to distinguish these benign artifacts from malicious patterns before they escalate into full-scale data exfiltration or system lockdown events in Azure Sentinel.

YARA Rule

rule PEncrypt10JunkCode
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 9C BE 00 10 40 00 8B FE B9 [4] BB 78 56 34 12 AD 33 C3 AB E2 FA 9D 61 E9 [3] FF }

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 4 specific false positive scenarios for the PEncrypt10JunkCode detection rule, including suggested filters and exclusions:

• Scenario: Automated Backup Encryption by Veeam or Commvault

  • Context: Enterprise backup agents (e.g., Veeam Backup & Replication or Commvault) frequently execute encryption routines that compress and obfuscate data streams. The YARA rule may misinterpret the high entropy of these encrypted backup chunks as “junk code” or malicious packing, triggering an alert every time a backup job runs.
  • Filter/Exclusion: Exclude processes running under the Veeam.Backup.Service.exe and CommServe.exe service accounts from the detection scope. Additionally, add a path exclusion for directories containing backup data (e.g., C:\ProgramData\Veeam\Backup or D:\Commvault\Content).

• Scenario: Scheduled Antivirus Cloud Scanning (CrowdStrike or Microsoft Defender)

  • Context: During scheduled cloud-based heuristic scans, security agents like CrowdStrike Falcon or Microsoft Defender often inject temporary encrypted modules to analyze file integrity. These modules can appear as obfuscated code blocks that match the “junk” signature of PEncrypt10JunkCode, particularly when scanning large archives (.zip, .7z).
  • Filter/Exclusion: Create a whitelist for the specific process names C-Service.exe (CrowdStrike) and MsMpEng.exe (Defender). Configure the rule to ignore alerts where the parent process is the antivirus service itself.

• Scenario: Software Deployment via SCCM or Intune

  • Context: When System Center Configuration Manager (SCCM) or Microsoft Intune pushes encrypted application packages (MSI/APPX) to endpoints, the deployment engine often unpacks and re-encrypts payloads in memory.