huntrule

Windows PowerShell Process Creation: COMPRESS OBFUSCATION with ASCII Encoding and DeflateStream

Flags PowerShell process creation command lines that use ASCII encoding plus compression/stream-reading patterns associated with obfuscation.

FreeReviewedSigma · Medium · v2
Product
windows
Category
process_creation
Author
Timur Zinniatullin, oscd.community (SigmaHQ), DRL 1.1
Published
2020-10-18
Updated
2026-07-31
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

Identifies PowerShell commands that include obfuscation-related patterns for data compression and ASCII encoding, specifically using DeflateStream and stream reading. Attackers may use these constructs to reduce readability of in-memory content and hinder analysis during execution. The rule relies on process creation telemetry, matching command-line substrings for PowerShell usage (new-object, ASCII encoding, DeflateStream, StreamReader, and ReadToEnd).

Reporting behind it

Related detections9 linkedT1027 — drag to rearrange
Suspicious PowerShell Invoke-Expression with Replace Obfuscation
Malicious Emmenhtal JavaScript Loader Spawning Encoded PowerShell
Suspicious Python Interpreter Launching Encoded PowerShell via subprocess
Suspicious PS1Bot PowerShell Payload Written to ProgramData (via file_event)
Malicious Non-Interactive Encoded PowerShell Stager (via process_creation)
Suspicious Hidden PowerShell Executing Substring of Dropped File
PowerShell Encoded or Download-Cradle Command Line (via process_creation)
Obfuscated Encoded PowerShell Payload Deployed - PowerShell (via powershell)
Suspicious PowerShell AES Decryption and Reflective Method Invocation in SolarMarker
Windows PowerShell Process Creation: COMPRESS OBFUSCATION with ASCII Encoding and DeflateStream
Pivot detection · T1027 · 9 related

Changelog

v2
  1. v2
    Candidate ingested via manual entry.2026-07-31
  2. 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.