PseudoSigner01REALBasicAnorganix

Hunt Hypothesis

This detection identifies potentially malicious or anomalous executables that exhibit pseudo-signing characteristics inconsistent with legitimate software signing patterns, as defined by the PseudoSigner01REALBasicAnorganix YARA rule. A SOC team should proactively hunt for these artifacts in Azure Sentinel to uncover sophisticated adversaries who leverage forged digital signatures to evade standard trust-based security controls and establish persistence within the environment.

YARA Rule

rule PseudoSigner01REALBasicAnorganix
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 89 E5 90 90 90 90 90 90 90 90 90 90 50 90 90 90 90 90 00 01 E9 }

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 PseudoSigner01REALBasicAnorganix detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Signature Updates

  • Context: The MsMpEng.exe process frequently executes signature definition updates via the Windows Update service. These updates often involve unpacking compressed archives containing non-standard binary structures that lack full cryptographic signatures during the initial extraction phase, triggering the “Anorganix” logic in the YARA rule.
  • Suggested Filter/Exclusion: Exclude processes where ProcessName equals MsMpEng.exe and CommandLine contains /update or references to the C:\ProgramData\Microsoft\Windows Defender\Platform directory.

• Scenario: Scheduled PowerShell Script Execution for Patch Management

  • Context: Enterprise administrators often deploy scheduled tasks (e.g., via SCCM or WSUS) that run custom .ps1 scripts to inventory hardware or apply hotfixes. These scripts may dynamically generate temporary executable wrappers or invoke native commands that do not adhere to the specific signing certificate chain expected by the rule, causing a false trigger during the System account’s nightly maintenance window.
  • Suggested Filter/Exclusion: Create an exclusion for events where UserAccount is SYSTEM and ProcessName matches powershell.exe, provided the execution path resides within the C:\Program Files\Microsoft Configuration Manager or a designated corporate script repository (e.g., \\fileserver\scripts\).

• Scenario: Visual Studio Build Artifacts in Development Environments

  • Context: In R&D departments, developers running local builds using Microsoft Visual Studio (devenv.exe) generate intermediate compilation artifacts. The build engine often spawns temporary processes to handle resource linking that utilize internal pseudo-signing mechanisms not recognized by