Suspicious PowerShell Execution with Base64 Encoded Command (Windows)

Alerts on PowerShell launched with Base64-encoded command-line parameters, excluding likely Guest Configuration noise.

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suspicious-powershell-execution-with-base64-encoded-command-windows-fb843269

title: Suspicious PowerShell Execution with Base64 Encoded Command (Windows)
id: 8c309b4a-d88a-49c4-a529-713e8508a836
status: test
description: This rule flags Windows process creations where PowerShell (powershell.exe or pwsh.exe) is launched with a Base64-style encoded command indicator in the command line (e.g., -e, -enc, -enco). Attackers commonly use encoded PowerShell to obscure malicious logic from casual inspection and simple string-based detections. The detection relies on process creation telemetry, matching the PowerShell executable name and specific command-line substrings while excluding events tied to known Guest Configuration worker execution paths and those containing an explicit -Encoding filter.
references:
  - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1059.001/T1059.001.md#atomic-test-20---powershell-invoke-known-malicious-cmdlets
  - https://unit42.paloaltonetworks.com/unit42-pulling-back-the-curtains-on-encodedcommand-powershell-attacks/
  - https://mikefrobbins.com/2017/06/15/simple-obfuscation-with-powershell-using-base64-encoding/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_powershell_encode.yml
author: frack113, Huntrule Team
date: 2022-01-02
modified: 2023-01-05
tags:
  - attack.execution
  - attack.t1059.001
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith:
      - \powershell.exe
      - \pwsh.exe
    CommandLine|contains:
      - " -e "
      - " -en "
      - " -enc "
      - " -enco"
      - " -ec "
  filter_encoding:
    CommandLine|contains: " -Encoding "
  filter_azure:
    ParentImage|contains:
      - C:\Packages\Plugins\Microsoft.GuestConfiguration.ConfigurationforWindows\
      - \gc_worker.exe
  condition: selection and not 1 of filter_*
falsepositives:
  - Unknown
level: medium
license: DRL-1.1
related:
  - id: fb843269-508c-4b76-8b8d-88679db22ce7
    type: derived

What it detects

This rule flags Windows process creations where PowerShell (powershell.exe or pwsh.exe) is launched with a Base64-style encoded command indicator in the command line (e.g., -e, -enc, -enco). Attackers commonly use encoded PowerShell to obscure malicious logic from casual inspection and simple string-based detections. The detection relies on process creation telemetry, matching the PowerShell executable name and specific command-line substrings while excluding events tied to known Guest Configuration worker execution paths and those containing an explicit -Encoding filter.

Known false positives

Unknown

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