detecting-suspicious-powershell-execution

name	detecting-suspicious-powershell-execution
description	Detect suspicious PowerShell execution patterns including encoded commands, download cradles, AMSI bypass attempts, and constrained language mode evasion.
domain	cybersecurity
subdomain	threat-hunting
tags	["threat-hunting","mitre-attack","powershell","execution","t1059","amsi","proactive-detection"]
version	1.0
author	mahipal
license	Apache-2.0
d3fend_techniques	["Executable Denylisting","Execution Isolation","File Metadata Consistency Validation","Content Format Conversion","File Content Analysis"]
nist_csf	["DE.CM-01","DE.AE-02","DE.AE-07","ID.RA-05"]

Detecting Suspicious Powershell Execution

When to Use

• When proactively hunting for indicators of detecting suspicious powershell execution in the environment
• After threat intelligence indicates active campaigns using these techniques
• During incident response to scope compromise related to these techniques
• When EDR or SIEM alerts trigger on related indicators
• During periodic security assessments and purple team exercises

Detection Gaps & Validation

• Script Block Logging (4104) is the ground truth: EID 4104 captures the deobfuscated script. With the GPO off you only have 4688/Sysmon EID 1 command lines, which obfuscation defeats — confirm 4104 and 4103 (Module Logging) are enabled and forwarded.
• -EncodedCommand and aliases: rules keyed on the literal powershell.exe -enc miss -e, -ec, pwsh, and renamed/copied binaries — match on EID 1 OriginalFileName = PowerShell.EXE plus base64 entropy, not the image name.
• AMSI bypass + downgrade: [Ref].Assembly...amsiInitFailed and -Version 2 downgrade attacks evade AMSI/4104; the Microsoft-Windows-PowerShell ETW provider can be patched out in-process — treat a host that suddenly stops emitting 4104 as suspicious, not clean.
• LOLBin proxies: IEX (New-Object Net.WebClient).DownloadString and execution via msbuild/installutil sidestep powershell.exe.
• Validate: run Atomic Red Team T1059.001 (encoded command + download cradle) and confirm the 4104 keyword and encoded-command searches fire.
• Tune FPs: SCCM, Intune, and admin automation generate encoded/long PowerShell — baseline by signing cert and parent (allow WmiPrvSE/ccmexec parents) before alerting.

Prerequisites

• EDR platform with process and network telemetry (CrowdStrike, MDE, SentinelOne)
• SIEM with relevant log data ingested (Splunk, Elastic, Sentinel)
• Sysmon deployed with comprehensive configuration
• Windows Security Event Log forwarding enabled
• Threat intelligence feeds for IOC correlation

Workflow

1. Formulate Hypothesis: Define a testable hypothesis based on threat intelligence or ATT&CK gap analysis.