hunting-for-anomalous-powershell-execution

name	hunting-for-anomalous-powershell-execution
description	Hunt for malicious PowerShell activity by analyzing Script Block Logging (Event 4104), Module Logging (Event 4103), and process creation events. The analyst parses Windows Event Log EVTX files to detect obfuscated commands, AMSI bypass attempts, encoded payloads, credential dumping keywords, and suspicious download cradles. Activates for requests involving PowerShell threat hunting, script block analysis, encoded command detection, or AMSI bypass identification.
domain	cybersecurity
subdomain	threat-hunting
tags	["powershell","script-block-logging","event-4104","amsi","threat-hunting","evtx","obfuscation"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["DE.CM-01","DE.AE-02","DE.AE-07","ID.RA-05"]

Hunting for Anomalous PowerShell Execution

Overview

PowerShell Script Block Logging (Event ID 4104) records the full deobfuscated script text executed on a Windows endpoint, making it the primary data source for hunting malicious PowerShell. Combined with Module Logging (4103) and process creation events, analysts can detect encoded commands, AMSI bypass patterns, download cradles, credential theft tools, and fileless attack techniques even when the attacker uses obfuscation layers.

When to Use

• When investigating security incidents that require hunting for anomalous powershell execution
• When building detection rules or threat hunting queries for this domain
• When SOC analysts need structured procedures for this analysis type
• When validating security monitoring coverage for related attack techniques

Detection Gaps & Validation

• 4104 must be on before the incident: Script Block Logging (EID 4104) only captures what was logged at execution time — if the GPO (Turn on PowerShell Script Block Logging) was off, no amount of EVTX parsing recovers the script. Module Logging (4103) and transcription complement but do not replace it.
• Multi-part script blocks: large/obfuscated scripts split across many 4104 records (MessageNumber/MessageTotal) — reassemble by ScriptBlock ID or you key on truncated fragments and miss the malicious section.
• ETW blinding & downgrade: amsiInitFailed, [Ref].Assembly ETW patching, and -Version 2 downgrade stop 4104 from being written at all — treat a host that stops emitting 4104 as suspicious, not clean.
• Non-powershell.exe hosts: runspaces hosted in System.Management.Automation.dll (C# loaders, InstallUtil, custom binaries) bypass powershell.exe — hunt the DLL load, not just the EXE.
• Validate: run Atomic Red Team T1059.001 (encoded command, IEX download cradle, AMSI bypass) on an instrumented host and confirm the parser flags 4104 records for amsi, FromBase64String, and DownloadString.
• Tune FPs: Intune/SCCM and admin automation produce long encoded scripts — baseline by initiating parent and signing, not script length alone.

Prerequisites

• Windows Event Log exports (.evtx) from Microsoft-Windows-PowerShell/Operational
• Python 3.8+ with python-evtx and lxml libraries