Windows PowerShell Base64-encoded shellcode in ScriptBlockText

Flags PowerShell script blocks containing Base64 strings matching known shellcode markers.

FreeReviewedSigma · High · v2

Product: windows
Category: ps_script
Author: David Ledbetter (shellcode), Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2018-11-17
Updated: 2026-07-31

ATT&CK techniques

Execution → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
- T1059.001PowerShell
Persistence
Priv Esc
- T1055Process Injection
Defense Evasion
- T1055Process Injection
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags PowerShell script block content that contains specific Base64-encoded sequences associated with embedded shellcode. Attackers may use Base64 to conceal payloads within otherwise normal-looking PowerShell execution, aiming to increase stealth. The detection relies on Script Block Logging telemetry by matching the presence of the defined encoded markers in the captured ScriptBlockText.

Reporting behind it

Related detections9 linkedT1059.001 — drag to rearrange

Suspicious Script Interpreter Spawned by Explorer via ClickFix Run Dialog (via process_creation)

Suspicious PowerShell Download Cradle via ClickFix Fake CAPTCHA (via process_creation)

Suspicious PowerShell EncodedCommand Spawned From Command Shell via Process Creation

Suspicious Script Download via Curl and PowerShell by Dohdoor

Malicious Mass Hyper-V Virtual Machine Shutdown via PowerShell by Kraken Ransomware

Suspicious PowerShell WebClient DownloadFile of Archive Payload (UAT-7237)

Suspicious SharePoint Worker Process Spawning Command Interpreter via ToolShell

Malicious Emmenhtal JavaScript Loader Spawning Encoded PowerShell

Suspicious Python Interpreter Launching Encoded PowerShell via subprocess

Windows PowerShell Base64-encoded shellcode in ScriptBlockText

Pivot detection · T1059.001 · 9 related

Changelog

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-powershell-base64-encoded-shellcode-in-script-block-text-16b37b70

title: Windows PowerShell Base64-encoded shellcode in ScriptBlockText
id: 0483279a-782e-4c3c-b814-4a05e5fab68a
status: test
description: This rule flags PowerShell script block content that contains specific Base64-encoded sequences associated with embedded shellcode. Attackers may use Base64 to conceal payloads within otherwise normal-looking PowerShell execution, aiming to increase stealth. The detection relies on Script Block Logging telemetry by matching the presence of the defined encoded markers in the captured ScriptBlockText.
references:
  - https://twitter.com/cyb3rops/status/1063072865992523776
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/powershell/powershell_script/posh_ps_shellcode_b64.yml
author: David Ledbetter (shellcode), Florian Roth (Nextron Systems), Huntrule Team
date: 2018-11-17
modified: 2024-01-25
tags:
  - attack.privilege-escalation
  - attack.stealth
  - attack.t1055
  - attack.execution
  - attack.t1059.001
logsource:
  product: windows
  category: ps_script
  definition: "Requirements: Script Block Logging must be enabled"
detection:
  selection:
    ScriptBlockText|contains:
      - OiCAAAAYInlM
      - OiJAAAAYInlM
  condition: selection
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 16b37b70-6fcf-4814-a092-c36bd3aafcbd
    type: derived

Convert

This rule as a query you can run. Uses no unlock credit.

SplunkSPL