Sigma rule: Regsvr32 DLL Execution With Uncommon Extension

Rule

Title

Regsvr32 DLL Execution With Uncommon Extension

Status

test

Level

medium

Author

Florian Roth (Nextron Systems)

Date

2019-07-17

Modified

2023-05-24

File

rules/windows/process_creation/proc_creation_win_regsvr32_uncommon_extension.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects a "regsvr32" execution where the DLL doesn't contain a common file extension.

Log source

product

windows

category

process_creation

Detection

selection:
    - Image|endswith: '\regsvr32.exe'
    - OriginalFileName: 'REGSVR32.EXE'
filter_main_legit_ext:
    CommandLine|contains:
        # Note: For better accuracy you might not want to use contains
        - '.ax'
        - '.cpl'
        - '.dll' # Covers ".dll.mui"
        - '.ocx'
filter_optional_pascal:
    CommandLine|contains: '.ppl'
filter_optional_avg:
    CommandLine|contains: '.bav'
filter_main_null_4688:
    CommandLine: null
filter_main_empty_4688:
    CommandLine: ''
condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*

False positives (as the rule lists them)

• Other legitimate extensions currently not in the list either from third party or specific Windows components.

Tags

• attack.privilege-escalation
• attack.persistence
• attack.stealth
• attack.t1574
• attack.execution

MITRE ATT&CK ids this rule names

• T1574

References

• https://app.any.run/tasks/34221348-072d-4b70-93f3-aa71f6ebecad/

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/process_creation/proc_creation_win_regsvr32_uncommon_extension.yml