PowerShell Net.WebClient DownloadFile/DownloadString Usage (Classic)

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 identifies PowerShell classic execution that uses the Net.WebClient class to download content via the .DownloadFile() or .DownloadString() methods. Downloading external content is a common step attackers use to obtain additional payloads or stage follow-on activity. Telemetry relies on PowerShell start logs capturing the script content that includes Net.WebClient and the specific download method calls.

Reporting behind it

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PowerShell Net.WebClient DownloadFile/DownloadString Usage (Classic)

Pivot detection · T1059.001 · 9 related

Changelog

v2

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

powershell-classic-net-webclient-download-via-downloadfile-downloadstring-3236fcd0

title: PowerShell Net.WebClient DownloadFile/DownloadString Usage (Classic)
id: 5439adb1-64fc-4ba6-86eb-df57032965df
related:
  - id: 65531a81-a694-4e31-ae04-f8ba5bc33759
    type: derived
  - id: 3236fcd0-b7e3-4433-b4f8-86ad61a9af2d
    type: derived
status: test
description: This rule identifies PowerShell classic execution that uses the Net.WebClient class to download content via the .DownloadFile() or .DownloadString() methods. Downloading external content is a common step attackers use to obtain additional payloads or stage follow-on activity. Telemetry relies on PowerShell start logs capturing the script content that includes Net.WebClient and the specific download method calls.
references:
  - https://www.trendmicro.com/en_us/research/22/j/lv-ransomware-exploits-proxyshell-in-attack.html
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/powershell/powershell_classic/posh_pc_download_via_webclient.yml
author: Florian Roth (Nextron Systems), Huntrule Team
date: 2017-03-05
modified: 2026-04-28
tags:
  - attack.execution
  - attack.command-and-control
  - attack.t1059.001
  - attack.t1105
logsource:
  product: windows
  category: ps_classic_start
detection:
  selection_webclient:
    Data|contains: Net.WebClient
  selection_download:
    Data|contains:
      - .DownloadFile(
      - .DownloadString(
  condition: all of selection_*
falsepositives:
  - This activity may be used by legitimate software, such as patch management tools or software updaters. Investigate any such activity and apply the necessary filter.
level: low
license: DRL-1.1

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