File With Uncommon Extension Created By An Office Application — Sigma Rule

Rule metadata and linked tags

Author: Vadim Khrykov (ThreatIntel), Cyb3rEng (Rule), Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: high. Source dates: 2021-08-23 / 2025-10-17.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 558f11b81947f1e232e4193527434fb89664c1ce597781e974952b05fcfd5849

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: File With Uncommon Extension Created By An Office Application
id: c7a74c80-ba5a-486e-9974-ab9e682bc5e4
status: test
description: Detects the creation of files with an executable or script extension by an Office application.
references:
    - https://thedfirreport.com/2021/03/29/sodinokibi-aka-revil-ransomware/
    - https://github.com/vadim-hunter/Detection-Ideas-Rules/blob/02bcbfc2bfb8b4da601bb30de0344ae453aa1afe/Threat%20Intelligence/The%20DFIR%20Report/20210329_Sodinokibi_(aka_REvil)_Ransomware.yaml
author: Vadim Khrykov (ThreatIntel), Cyb3rEng (Rule), Nasreddine Bencherchali (Nextron Systems)
date: 2021-08-23
modified: 2025-10-17
tags:
    - attack.t1204.002
    - attack.execution
logsource:
    product: windows
    category: file_event
detection:
    # Note: Please add more file extensions to the logic of your choice.
    selection1:
        Image|endswith:
            - '\excel.exe'
            - '\msaccess.exe'
            - '\mspub.exe'
            - '\powerpnt.exe'
            - '\visio.exe'
            - '\winword.exe'
    selection2:
        TargetFilename|endswith:
            - '.bat'
            - '.cmd'
            - '.com'
            - '.dll'
            - '.exe'
            - '.hta'
            - '.ocx'
            - '.proj'
            - '.ps1'
            - '.scf'
            - '.scr'
            - '.sys'
            - '.vbe'
            - '.vbs'
            - '.wsf'
            - '.wsh'
    filter_main_localassembly:
        TargetFilename|contains: '\AppData\Local\assembly\tmp\'
        TargetFilename|endswith: '.dll'
    filter_optional_webservicecache: # matches e.g. directory with name *.microsoft.com
        TargetFilename|contains|all:
            - 'C:\Users\'
            - '\AppData\Local\Microsoft\Office\'
            - '\WebServiceCache\AllUsers'
        TargetFilename|endswith: '.com'
    filter_optional_webex:
        Image|endswith: '\winword.exe'
        TargetFilename|contains: '\AppData\Local\Temp\webexdelta\'
        TargetFilename|endswith:
            - '.dll'
            - '.exe'
    filter_optional_backstageinappnavcache: # matches e.g. C:\Users\xxxxx\AppData\Local\Microsoft\Office\16.0\BackstageInAppNavCache\ODB-user@domain.com
        TargetFilename|contains|all:
            - 'C:\Users\'
            - '\AppData\Local\Microsoft\Office\'
            - '\BackstageInAppNavCache\'
        TargetFilename|endswith: '.com'
    condition: all of selection* and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://thedfirreport.com/2021/03/29/sodinokibi-aka-revil-ransomware/
• https://github.com/vadim-hunter/Detection-Ideas-Rules/blob/02bcbfc2bfb8b4da601bb30de0344ae453aa1afe/Threat%20Intelligence/The%20DFIR%20Report/20210329_Sodinokibi_(aka_REvil)_Ransomware.yaml