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Detection rules › Sigma

Change User Agents with WebRequest

Status
test
Severity
medium
Log source
product windows, category ps_script
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

TacticTechniques
Command & ControlT1071.001 Application Layer Protocol: Web Protocols

Event coverage

ProviderEventTitle
PowerShellEvent ID 4104Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body yaml

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

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
ScriptBlockTextmatch
  • 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)