huntrule

Windows Process Execution: Suspicious PowerShell Encoded Command with Exec Bypass

Flags Windows process creations with a bypass-and-encoded PowerShell Start-Job command-line pattern linked to Mercury-related activity.

FreeReviewedSigma · High · v5
Product
windows
Category
process_creation
Author
Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2022-08-26
Updated
2026-07-31
AnalysisDetection

ATT&CK techniques

Execution

  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 flags Windows process creation events whose command line contains both an execution bypass string and a specific encoded payload consistent with a Start-Job script block. Attackers may use execution bypass and encoded PowerShell to evade command-line inspection and run malicious logic indirectly. The detection relies on process_creation telemetry with the full CommandLine field and matches the required substrings as defined in the rule.

Reporting behind it

Related detections9 linkedT1059.001 — drag to rearrange
Suspicious IIS Worker Process Spawning Command or Scripting Interpreter via SharePoint ToolShell Exploitation (via process_creation)
Suspicious PowerShell Download Cradle Spawned from Explorer via ClickFix Lure (via process_creation)
Malicious Interlock RAT FileFix Download-Cradle via PowerShell WebClient with PowerShell User-Agent (via ps_script)
Malicious Metasploit Stager Delivery via mshta Remote HTA (via process_creation)
Suspicious PowerShell Download of Disguised Payload to ProgramData
Suspicious PowerShell WebClient Download of Executable Payload
Malicious Script Host Spawning PowerShell in Gootloader Chain
Suspicious PsExec Service Launching Encoded PowerShell Payload
Suspicious PowerShell Remote Script Execution via IEX DownloadString
Windows Process Execution: Suspicious PowerShell Encoded Command with Exec Bypass
Pivot detection · T1059.001 · 9 related

Changelog

v5
  1. v5
    Candidate ingested via manual entry.2026-07-31
  2. v4
    Candidate ingested via manual entry.2026-07-31
  3. v3
    Candidate ingested via manual entry.2026-07-31
  4. v2
    Candidate ingested via manual entry.2026-07-31
  5. v1
    No changelog recorded for this version.2026-07-30

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