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

Analysis Detection

ATT&CK techniques

Execution

Recon
Resource Dev
Initial Access
Execution
- T1059.001PowerShell
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
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

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Windows Process Execution: Suspicious PowerShell Encoded Command with Exec Bypass

Pivot detection · T1059.001 · 9 related

Changelog

v5
Candidate ingested via manual entry.2026-07-31
v4
Candidate ingested via manual entry.2026-07-31
v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
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.

windows-process-creation-detects-suspicious-powershell-command-line-for-mercury--a62298a3

title: "Windows Process Execution: Suspicious PowerShell Encoded Command with Exec Bypass"
id: 410e1216-9e8b-4695-bf33-f08a40143694
status: test
description: 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.
references:
  - https://www.microsoft.com/security/blog/2022/08/25/mercury-leveraging-log4j-2-vulnerabilities-in-unpatched-systems-to-target-israeli-organizations/
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2022/TA/MERCURY/proc_creation_win_apt_mercury.yml
author: Florian Roth (Nextron Systems), Huntrule Team
date: 2022-08-26
modified: 2023-03-10
tags:
  - attack.execution
  - attack.t1059.001
  - attack.g0069
  - detection.emerging-threats
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    CommandLine|contains|all:
      - -exec bypass -w 1 -enc
      - UwB0AGEAcgB0AC0ASgBvAGIAIAAtAFMAYwByAGkAcAB0AEIAbABvAGMAawAgAHsAKABzAGEAcABzACAAKAAiAHAA
  condition: selection
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: a62298a3-1fe0-422f-9a68-ffbcbc5a123d
    type: derived

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