huntrule

Suspicious PowerShell Spawned from PyInstaller MEI Extraction Folder (via process_creation)

PremiumReviewedSigma · Medium · v1
Product
windows
Category
process_creation
Author
HuntRule
Published
2026-09-21
Updated
2026-09-21
AnalysisDetection

ATT&CK techniques

Execution → Defense Evasion

  1. Recon

  2. Resource Dev

  3. Initial Access

  4. Execution

  5. Persistence

  6. Priv Esc

  7. Defense Evasion

  8. Cred Access

  9. Discovery

  10. Lateral Movement

  11. Collection

  12. C2

  13. Exfiltration

  14. Impact

What it detects

This rule detects powershell.exe spawned by a process running from a PyInstaller _MEI extraction folder under the user Temp directory, matching SolarMarker's shift to PyInstaller-packed loaders. The bundled Python script decodes base64 and invokes PowerShell with a hidden window, so a PowerShell child of a _MEI process is anomalous. This stages the SolarMarker backdoor.

Reporting behind it

Related detections9 linkedT1027 — drag to rearrange
Suspicious PowerShell Encoded Command Execution
Suspicious PowerShell Invoke-Expression with Replace Obfuscation
Malicious Emmenhtal JavaScript Loader Spawning Encoded PowerShell
Suspicious Python Interpreter Launching Encoded PowerShell via subprocess
Suspicious PS1Bot PowerShell Payload Written to ProgramData (via file_event)
Malicious Non-Interactive Encoded PowerShell Stager (via process_creation)
Suspicious Hidden PowerShell Executing Substring of Dropped File
PowerShell Encoded or Download-Cradle Command Line (via process_creation)
Obfuscated Encoded PowerShell Payload Deployed - PowerShell (via powershell)
Suspicious PowerShell Spawned from PyInstaller MEI Extraction Folder (via process_creation)
Pivot detection · T1027 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.