huntrule

Suspicious Encoded PowerShell Using Base64 Stream Decompression Routines (via process_creation)

PremiumReviewedSigma · Medium · v1
Product
windows
Category
process_creation
Author
HuntRule
Published
2026-10-23
Updated
2026-10-23
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 command lines combining base64 decoding with stream decompression routines that Red Canary tied to obfuscated loaders staging Cobalt Strike during a hospital ransomware attack. Adversaries chain FromBase64String with stream decompression to unpack in-memory payloads, so these combined tokens reveal obfuscated execution that plain string matching would miss.

Reporting behind it

Related detections9 linkedT1027 — drag to rearrange
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 String Concatenation Obfuscation for Batch Extension via LNK (via process_creation)
Suspicious PowerShell Spawned from PyInstaller MEI Extraction Folder (via process_creation)
Suspicious PowerShell Encoded Command Execution
Suspicious PowerShell Invoke-Expression with Replace Obfuscation
Malicious Emmenhtal JavaScript Loader Spawning Encoded PowerShell
Suspicious Encoded PowerShell Using Base64 Stream Decompression Routines (via process_creation)
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.