huntrule

Suspicious PowerShell Invoke-Expression with Replace Obfuscation

PremiumReviewedSigma · Medium · v1
Product
windows
Category
ps_script
Author
HuntRule
Published
2026-09-14
Updated
2026-09-14
AnalysisDetection

ATT&CK techniques

Execution → Defense Evasion

  1. Recon

  2. Resource Dev

  3. Initial Access

  4. Execution

  5. Persistence

  6. Priv Esc

  7. Defense Evasion

  8. Cred Access

  9. Discovery

  10. Lateral Movement

  11. Collection

  12. C2

  13. Exfiltration

  14. Impact

What it detects

This rule detects PowerShell script content that combines Invoke-Expression with the -replace operator using mixed-case obfuscation, a deobfuscation-then-execute pattern used by GootLoader. Attackers scramble the payload string and reconstruct it at runtime to evade static detection before executing it in memory. The IEX plus -replace combination is a strong indicator of obfuscated in-memory execution.

Reporting behind it

Related detections9 linkedT1027 — drag to rearrange
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Suspicious Encoded PowerShell Using Base64 Stream Decompression Routines (via process_creation)
Suspicious PowerShell In-Memory Execution with AES Decryption
Suspicious Encoded PowerShell Command Execution
Suspicious PEAKLIGHT Memory-Only PowerShell Downloader Flags (via process_creation)
Obfuscated PowerShell Script: Indirect Cmdlet Execution via ExportedCommands Array Index
Suspicious PowerShell Invoke-Expression with Replace Obfuscation
Pivot detection · T1027 · 9 related

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