PCPEEncryptorAlphapreview

Hunt Hypothesis

This hunt hypothesis targets adversaries utilizing custom encryption mechanisms or preview-stage encryptors that may indicate early-stage ransomware activity or data exfiltration attempts. Proactively hunting for these specific YARA signatures in Azure Sentinel allows the SOC team to identify and analyze potential threats before they escalate, ensuring rapid response to novel encryption behaviors that standard rules might miss.

YARA Rule

rule PCPEEncryptorAlphapreview
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 53 51 52 56 57 55 E8 00 00 00 00 5D 8B CD 81 ED 33 30 40 ?? 2B 8D EE 32 40 00 83 E9 0B 89 8D F2 32 40 ?? 80 BD D1 32 40 ?? 01 0F 84 }

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 3-5 specific false positive scenarios for the PCPEEncryptorAlphapreview detection rule, along with suggested filters and exclusions:

• Scenario: Legitimate execution of Microsoft Office Click-to-Run updates or background repair tasks.

  • Context: The OfficeClickToRun.exe process often triggers encryption-related behaviors during patching sessions, mimicking the signature of a PCPE encryptor. This frequently occurs on user workstations between 02:00 and 04:00 local time.
  • Suggested Filter/Exclusion: Exclude processes where ImageFileName equals OfficeClickToRun.exe AND CommandLine contains keywords like “update”, “repair”, or “install”. Additionally, restrict the rule to exclude execution paths within C:\Program Files\Microsoft Office\root\Office16.

• Scenario: Scheduled backup jobs utilizing Veeam Agent for Microsoft Windows.

  • Context: When Veeam performs incremental backups on file servers, its engine (VeeamAgent.exe or vagent.exe) encrypts metadata and temporary cache files using algorithms that overlap with the PCPE signature. This is common during nightly maintenance windows (e.g., 20:00–23:00).
  • Suggested Filter/Exclusion: Create an exclusion for processes running under the Veeam service account (NT SERVICE\VeeamAgent) or filter by image path containing C:\Program Files\Microsoft Veeam Agent.

• Scenario: Deployment of enterprise-wide Endpoint Protection policies via CrowdStrike Falcon.

  • Context: The CrowdStrike sensor (csagent.exe) performs real-time scanning and policy updates that involve encrypting configuration blobs. During the initial rollout of a new “Alpha” preview policy, this activity spikes across the domain controller and management