Regsvr32 DLL Execution With Suspicious File Extension — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems), frack113. Source status: test; severity: high. Source dates: 2021-11-29 / 2025-08-27.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 785c363779a2379ec33fefe2ee631e87460f61e0e579a813e9dfa81915bdbb4e

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: Regsvr32 DLL Execution With Suspicious File Extension
id: 089fc3d2-71e8-4763-a8a5-c97fbb0a403e
related:
    - id: 8e2b24c9-4add-46a0-b4bb-0057b4e6187d
      type: obsolete
status: test
description: Detects the execution of REGSVR32.exe with DLL files masquerading as other files
references:
    - https://thedfirreport.com/2021/11/29/continuing-the-bazar-ransomware-story/
    - https://blog.talosintelligence.com/2021/10/threat-hunting-in-large-datasets-by.html
    - https://guides.lib.umich.edu/c.php?g=282942&p=1885348
    - https://harfanglab.io/insidethelab/uac-0057-pressure-ukraine-poland/
author: Florian Roth (Nextron Systems), frack113
date: 2021-11-29
modified: 2025-08-27
tags:
    - attack.stealth
    - attack.t1218.010
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\regsvr32.exe'
        - OriginalFileName: 'REGSVR32.EXE'
    selection_cli:
        CommandLine|endswith:
            # Add more image extensions
            # https://twitter.com/Max_Mal_/status/1542461200797163522/photo/3
            - '.bin'
            - '.bmp'
            - '.cr2'
            - '.dat'
            - '.eps'
            - '.gif'
            - '.ico'
            - '.jpeg'
            - '.jpg'
            - '.log'
            - '.nef'
            - '.orf'
            - '.png'
            - '.raw'
            - '.rtf'
            - '.sr2'
            - '.temp'
            - '.tif'
            - '.tiff'
            - '.tmp'
            - '.txt'
    condition: all of selection_*
falsepositives:
    - Unlikely
level: high

Original YAML and metadata in JSON

False positives

• Unlikely

Source references

• https://thedfirreport.com/2021/11/29/continuing-the-bazar-ransomware-story/
• https://blog.talosintelligence.com/2021/10/threat-hunting-in-large-datasets-by.html
• https://guides.lib.umich.edu/c.php?g=282942&p=1885348
• https://harfanglab.io/insidethelab/uac-0057-pressure-ukraine-poland/