Creation of WerFault.exe/Wer.dll in Unusual Folder — Sigma Rule

Rule metadata and linked tags

Author: frack113. Source status: test; severity: medium. Source dates: 2022-05-09 / 2026-05-18.

{
  "product": "windows",
  "category": "file_event"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: edc6a08b945eb5cd13101a2499395728a86d45e1bb4e9b010915aabb8f899dc8

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Creation of WerFault.exe/Wer.dll in Unusual Folder
id: 28a452f3-786c-4fd8-b8f2-bddbe9d616d1
status: test
description: Detects the creation of a file named "WerFault.exe" or "wer.dll" in an uncommon folder, which could be a sign of WerFault DLL hijacking.
references:
    - https://www.bleepingcomputer.com/news/security/hackers-are-now-hiding-malware-in-windows-event-logs/
author: frack113
date: 2022-05-09
modified: 2026-05-18
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.execution
    - attack.stealth
    - attack.t1574.001
logsource:
    product: windows
    category: file_event
detection:
    selection:
        TargetFilename|endswith:
            - '\WerFault.exe'
            - '\wer.dll'
    filter_main_known_locations:
        TargetFilename|startswith:
            - 'C:\Windows\SoftwareDistribution\'
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
            - 'C:\Windows\WinSxS\'
            - 'C:\Windows\UUS\' # covers both C:\Windows\UUS\arm64\ and C:\Windows\UUS\packages\
    filter_main_process:
        Image|endswith: '\wuaucltcore.exe'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://www.bleepingcomputer.com/news/security/hackers-are-now-hiding-malware-in-windows-event-logs/