PEPasswordv02SMTSMF

Hunt Hypothesis

This detection identifies potentially malicious Portable Executable (PE) files containing specific password-related indicators that may signal an adversary’s attempt to harvest credentials or establish persistence through customized binaries. Proactively hunting for these artifacts in Azure Sentinel is essential to uncover low-severity anomalies that could represent early-stage reconnaissance or lateral movement activities often missed by standard alerting thresholds.

YARA Rule

rule PEPasswordv02SMTSMF
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 04 [3] 8B EC 5D C3 33 C0 5D 8B FD 81 ED 33 26 40 ?? 81 EF [4] 83 EF 05 89 AD 88 27 40 ?? 8D 9D 07 29 40 ?? 8D B5 62 28 40 ?? 46 80 }

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 PEPasswordv02SMTSMF detection rule, along with suggested filters and exclusions:

• Scenario: Automated Password Rotation via Microsoft Endpoint Configuration Manager (SCCM)

  • Context: The SCCM client service (ccmexec.exe) or the associated SMS Agent Host performs scheduled password updates for local service accounts or domain users. This process often invokes the smssvcs (System Management Service) to handle secure memory transfers, triggering the YARA signature due to legitimate PE file manipulation and SMTS (Secure Memory Transfer Service) interactions.
  • Filter/Exclusion: Create an exclusion for processes where the parent is ccmexec.exe or SMS Agent Host running on specific SCCM management points. Exclude paths matching C:\Program Files\Microsoft Configuration Manager\*.

• Scenario: Windows Update Service (WUClient) Patch Deployment

  • Context: During major cumulative updates, the Windows Update client (wuauclt.exe) or the Background Intelligent Transfer Service (bitsadmin.exe) may invoke password-related security modules to update credentials for update servers. The YARA rule detects these legitimate memory transfers as potential anomalies when the system writes encrypted configuration data involving PE headers.
  • Filter/Exclusion: Exclude events where the process image path contains C:\Windows\System32\ and the process name is wuauclt.exe, bitsadmin.exe, or usoc.dll. Additionally, filter out events occurring during standard maintenance windows (e.g., 01:00–05:00 local time).

• Scenario: Active Directory Password Policy Enforcement via PowerShell Scripts

  • Context: IT administrators frequently run scheduled PowerShell jobs (powershell.exe) to enforce password policies, reset service account passwords, or migrate user profiles.