Windows Browser-Injected rundll32 Execution Indicative of GuLoader Activity

Flags rundll32.exe being launched from a browser process, matching GuLoader-style injected browser execution behavior on Windows.

FreeReviewedSigma · High · v5

Product: windows
Category: process_creation
Author: @kostastsale (SigmaHQ), DRL 1.1
Published: 2023-08-07
Updated: 2026-07-31

Analysis Detection

ATT&CK techniques

Priv Esc → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
- T1055Process Injection
Defense Evasion
- T1055Process Injection
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule matches process creation where a rundll32.exe instance is spawned with its command line ending in \rundll32.exe and the parent process image is a browser (chrome.exe, firefox.exe, or msedge.exe). It is intended to flag GuLoader-style behavior where malware executes via a browser-injected process path and then initiates activity through rundll32. Detection relies on Windows process creation telemetry including parent image, child image, and command line fields.

Reporting behind it

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Windows Browser-Injected rundll32 Execution Indicative of GuLoader Activity

Pivot detection · T1055 · 9 related

Changelog

v5
Candidate ingested via manual entry.2026-07-31
v4
Candidate ingested via manual entry.2026-07-31
v3
Candidate ingested via manual entry.2026-07-31
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.

guloader-activity-injected-browser-parent-spawns-rundll32-exe-on-windows-89e1490f

title: Windows Browser-Injected rundll32 Execution Indicative of GuLoader Activity
id: 5a500cb2-963a-41ed-9997-ec343142521e
status: test
description: This rule matches process creation where a rundll32.exe instance is spawned with its command line ending in \rundll32.exe and the parent process image is a browser (chrome.exe, firefox.exe, or msedge.exe). It is intended to flag GuLoader-style behavior where malware executes via a browser-injected process path and then initiates activity through rundll32. Detection relies on Windows process creation telemetry including parent image, child image, and command line fields.
references:
  - Internal Research
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2023/Malware/GuLoader/proc_creation_win_malware_guloader_execution.yml
author: "@kostastsale, Huntrule Team"
date: 2023-08-07
tags:
  - attack.privilege-escalation
  - attack.stealth
  - attack.t1055
  - detection.emerging-threats
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    ParentImage|endswith:
      - \chrome.exe
      - \firefox.exe
      - \msedge.exe
    Image|endswith: \rundll32.exe
    CommandLine|endswith: \rundll32.exe
  condition: selection
falsepositives:
  - Unlikely
level: high
license: DRL-1.1
related:
  - id: 89e1490f-1a3e-452a-bbb8-b68a5f58072f
    type: derived

Convert

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