Injected Browser Process Spawning Rundll32 - GuLoader Activity

Status: test
Severity: high
Log source: category process_creation, product windows
Author: @kostastsale
Source: github.com/SigmaHQ/sigma

Detects the execution of installed GuLoader malware on the host. GuLoader is initiating network connections via the rundll32.exe process that is spawned via a browser parent(injected) process.

Known false positives

Unlikely

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1055` Process Injection
Stealth	`T1055` Process Injection

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Injected Browser Process Spawning Rundll32 - GuLoader Activity
id: 89e1490f-1a3e-452a-bbb8-b68a5f58072f
status: test
description: |
    Detects the execution of installed GuLoader malware on the host.
    GuLoader is initiating network connections via the rundll32.exe process that is spawned via a browser parent(injected) process.
references:
    - Internal Research
author: '@kostastsale'
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

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    ParentImage|endswith:
        - '\chrome.exe'
        - '\firefox.exe'
        - '\msedge.exe'
    Image|endswith: '\rundll32.exe'
    CommandLine|endswith: '\rundll32.exe'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	ends_with	`\rundll32.exe` corpus 3 (sigma 3)	`field:"CommandLine" kind:ends_with value:"\rundll32.exe"`
`Image`	ends_with	`\rundll32.exe` corpus 94 (sigma 94)	`field:"Image" kind:ends_with value:"\rundll32.exe"`
`ParentImage`	ends_with	`\chrome.exe` corpus 5 (sigma 5) `\firefox.exe` corpus 4 (sigma 4) `\msedge.exe` corpus 4 (sigma 4)	`field:"ParentImage" kind:ends_with`