Sigma rule: File With Uncommon Extension Created By An Office Application

Rule

Title

File With Uncommon Extension Created By An Office Application

Status

test

Level

high

Author

Vadim Khrykov (ThreatIntel), Cyb3rEng (Rule), Nasreddine Bencherchali (Nextron Systems)

Date

2021-08-23

Modified

2025-10-17

File

rules/windows/file/file_event/file_event_win_office_susp_file_extension.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects the creation of files with an executable or script extension by an Office application.

Log source

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\[email protected]
    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_*

False positives (as the rule lists them)

• Unknown

Tags

• attack.t1204.002
• attack.execution

MITRE ATT&CK ids this rule names

• T1204.002

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

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/file/file_event/file_event_win_office_susp_file_extension.yml