PESpinv0b

Hunt Hypothesis

This detection identifies potential malicious activity associated with the PESpinv0b signature, which may indicate an adversary leveraging specific file characteristics or runtime behaviors to establish a foothold within the environment. Proactive hunting for this indicator in Azure Sentinel is essential to uncover low-severity anomalies that could represent early-stage threats, allowing the SOC team to investigate and mitigate risks before they escalate into significant incidents.

YARA Rule

rule PESpinv0b
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 01 68 60 E8 00 00 00 00 8B 1C 24 83 C3 12 81 2B E8 B1 06 00 FE 4B FD 82 2C 24 72 C8 46 00 0B E4 74 9E 75 01 C7 81 73 04 D7 7A F7 2F 81 73 19 77 00 43 B7 F6 C3 6B B7 00 00 F9 FF E3 C9 C2 08 00 A3 68 72 01 FF 5D 33 C9 41 E2 26 E8 01 00 00 00 EA 5A 33 C9 }

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 PESpinv0b detection rule, including suggested filters and exclusions tailored for a legitimate enterprise environment:

• Scenario: Scheduled Antivirus Definition Updates

  • Context: The YARA rule may flag the background process of major security suites (e.g., Microsoft Defender, CrowdStrike Falcon) when they spin up to download or apply new signature definitions. These processes often inject code into system memory that mimics the behavior of an unknown process spawning.
  • Filter/Exclusion: Exclude processes matching *defender.exe, *falcon.sys, and *ccSvcHst.exe (Symantec) when running under the context of scheduled tasks named “Antivirus Update” or “Definition Sync”.

• Scenario: Enterprise Endpoint Management Agent Activity

  • Context: Tools like Microsoft Intune, Jamf Pro, or SCCM (Configuration Manager) frequently spawn child processes to perform inventory scans, software deployments, or policy enforcement. These agents often execute scripts that trigger the PESpinv0b logic due to dynamic process creation patterns.
  • Filter/Exclusion: Create an exclusion for parent processes named IntuneManagementExtension.exe, ccmexec.exe, and jamfagentd. Additionally, filter out events where the command line contains keywords like “inventory,” “deployment,” or “policy-refresh.”

• Scenario: Automated Backup and Archiving Jobs

  • Context: Scheduled backup solutions such as Veeam Agent, Acronis Cyber Protect, or Rubrik often spawn temporary worker processes to compress data or manage snapshots. These workers may exhibit memory injection behaviors that the YARA rule interprets as suspicious process spawning.
  • Filter/Exclusion: Exclude file paths located within standard backup installation directories (e