Malicious PowerShell IEX DownloadString One-Liner

ATT&CK techniques

Execution → C2

Recon
Resource Dev
Initial Access
Execution
- T1059.001PowerShell
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
- T1105Ingress Tool Transfer
Exfiltration
Impact

What it detects

This rule detects PowerShell using Invoke-Expression together with a WebClient DownloadString call to fetch and run remote code in memory. This one-liner is delivered through the Win+R fake CAPTCHA lure used to distribute Lumma Stealer. Catching the fetch-and-execute pattern flags fileless staging before the stealer touches disk.

Reporting behind it

Related detections9 linkedT1059.001 — drag to rearrange

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Malicious Cloud Atlas PowerShell Download Cradle via IEX WebClient (via process_creation)

Suspicious PowerShell Downloader Spawned by Batch Script (via process_creation)

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Suspicious PowerShell Download of scrss or ekrn Masquerading Scripts

Malicious PowerShell IEX DownloadString One-Liner

Pivot detection · T1059.001 · 9 related

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

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