PENinjamodified

Hunt Hypothesis

This rule detects the presence of a modified version of the PENinja tool, a popular open-source penetration testing utility that adversaries may repurpose for reconnaissance or lateral movement within the environment. Proactively hunting for this artifact in Azure Sentinel allows the SOC to identify potential unauthorized testing activities or compromised endpoints where attackers have deployed familiar tools to blend in with legitimate administrative tasks.

YARA Rule

rule PENinjamodified
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 5D 8B C5 81 ED B2 2C 40 00 2B 85 94 3E 40 00 2D 71 02 00 00 89 85 98 3E 40 00 0F B6 B5 9C 3E 40 00 8B FD }

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: A legacy .NET application or Java-based service (e.g., Apache Tomcat, Spring Boot) uses System.Reflection to dynamically load custom classes or perform runtime code analysis for plugin architectures.
  • Filter/Exclusion: Exclude processes where the parent process is a known JVM or .NET host (e.g., java.exe, dotnet.exe, w3wp.exe) and the loaded module name contains common framework identifiers like System.Core.dll, mscorlib.dll, or libjvm.dll.
• Scenario: Enterprise endpoint protection agents (e.g., CrowdStrike Falcon, Carbon Black, SentinelOne) or EDR tools inject themselves into target processes to monitor API calls, often using NtLoadDriver or reflection-based injection techniques to maintain stealth.
  • Filter/Exclusion: Exclude events where the source process is a known EDR/AV service executable (e.g., FalconSensor.exe, cb.exe, SentinelOneAgent.exe) or where the injection target is a system process (e.g., svchost.exe, csrss.exe) initiated by a trusted service account.
• Scenario: Scheduled maintenance jobs or backup software (e.g., Veeam, Commvault, Acronis) use reflection to dynamically load backup drivers or snapshot modules during nightly backups, especially when interacting with virtualization layers.
  • Filter/Exclusion: Exclude processes running under a dedicated backup service account (e.g., svc_backup, backup_admin) and where the command line or process path contains keywords like backup, snapshot, or agent (e.g., VeeamBackup.exe, CommvaultAgent.exe).
• Scenario: Development or testing environments where developers run unit tests or integration tests using frameworks like JUnit, NUnit, or xUnit, which heavily rely on reflection to instantiate