huntrule

PowerShell ScriptBlock WebClient Download Calls

Alert on PowerShell ScriptBlock text that uses System.Net.WebClient to download files or strings from the Internet.

FreeReviewedSigma · Medium · v2
Product
windows
Category
ps_script
Author
Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2017-03-05
Updated
2026-07-31
AnalysisDetection

ATT&CK techniques

Execution

  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 flags PowerShell activity where a ScriptBlock contains references to System.Net.WebClient and download-related method calls such as DownloadFile, DownloadFileAsync, DownloadString, or DownloadStringAsync. Attackers commonly use these .NET WebClient methods to pull additional code or payload content into a PowerShell session. The detection relies on Script Block Logging telemetry that includes the ScriptBlockText content.

Reporting behind it

Related detections9 linkedT1059.001 — drag to rearrange
Malicious Metasploit Stager Delivery via mshta Remote HTA (via process_creation)
Suspicious PowerShell Download of Disguised Payload to ProgramData
Suspicious PowerShell WebClient Download of Executable Payload
Malicious Script Host Spawning PowerShell in Gootloader Chain
Suspicious PsExec Service Launching Encoded PowerShell Payload
Suspicious PowerShell Remote Script Execution via IEX DownloadString
Malicious SharePoint ToolShell Post-Exploitation via Encoded PowerShell (via process_creation)
Suspicious In-Memory PowerShell Execution from Web Server via Automation Assembly (via image_load)
Malicious Qilin Chrome Credential Harvesting Script Execution via IPScanner (via process_creation)
PowerShell ScriptBlock WebClient Download Calls
Pivot detection · T1059.001 · 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.