Regsvr32 DLL Execution With Uncommon Extension

 1title: Regsvr32 DLL Execution With Uncommon Extension
 2id: 50919691-7302-437f-8e10-1fe088afa145
 3status: test
 4description: Detects a "regsvr32" execution where the DLL doesn't contain a common file extension.
 5references:
 6    - https://app.any.run/tasks/34221348-072d-4b70-93f3-aa71f6ebecad/
 7author: Florian Roth (Nextron Systems)
 8date: 2019/07/17
 9modified: 2023/05/24
10tags:
11    - attack.defense_evasion
12    - attack.t1574
13    - attack.execution
14logsource:
15    category: process_creation
16    product: windows
17detection:
18    selection:
19        - Image|endswith: '\regsvr32.exe'
20        - OriginalFileName: 'REGSVR32.EXE'
21    filter_main_legit_ext:
22        CommandLine|contains:
23            # Note: For better accuracy you might not want to use contains
24            - '.ax'
25            - '.cpl'
26            - '.dll' # Covers ".dll.mui"
27            - '.ocx'
28    filter_optional_pascal:
29        CommandLine|contains: '.ppl'
30    filter_optional_avg:
31        CommandLine|contains: '.bav'
32    filter_main_null_4688:
33        CommandLine: null
34    filter_main_empty_4688:
35        CommandLine: ''
36    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
37falsepositives:
38    - Other legitimate extensions currently not in the list either from third party or specific Windows components.
39level: medium