Change User Agents with WebRequest

Status: test
Severity: medium
Log source: category ps_script, product windows
Author: frack113
Source: github.com/SigmaHQ/sigma

Adversaries may communicate using application layer protocols associated with web traffic to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1071.001` Application Layer Protocol: Web Protocols

Telemetry coverage

Provider	Record / event type
PowerShell	Event ID 4104: Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body

title: Change User Agents with WebRequest
id: d4488827-73af-4f8d-9244-7b7662ef046e
status: test
description: |
    Adversaries may communicate using application layer protocols associated with web traffic to avoid detection/network filtering by blending in with existing traffic.
    Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1071.001/T1071.001.md#t1071001---web-protocols
author: frack113
date: 2022-01-23
modified: 2025-07-18
tags:
    - attack.command-and-control
    - attack.t1071.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection_webrequest:
        ScriptBlockText|contains:
            - 'Invoke-WebRequest'
            - 'Invoke-RestMethod'
            - ' irm ' # Space before and after to avoid false positives with 'irm' as a variable
            - 'iwr '
    selection_useragent:
        ScriptBlockText|contains: '-UserAgent '
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_webrequest`

selection_webrequest:
    ScriptBlockText|contains:
        - 'Invoke-WebRequest'
        - 'Invoke-RestMethod'
        - ' irm '
        - 'iwr '

Stage 2: `selection_useragent`

selection_useragent:
    ScriptBlockText|contains: '-UserAgent '

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ScriptBlockText`	match	`irm` corpus 2 (sigma 2) `-UserAgent` `Invoke-RestMethod` corpus 4 (sigma 3, splunk 1) `Invoke-WebRequest` corpus 3 (sigma 3) `iwr` corpus 3 (sigma 3)	`field:"ScriptBlockText" kind:match`