Regsvr32 DLL Execution With Uncommon Extension

Title: Regsvr32 DLL Execution With Uncommon Extension
Status: test
Description:Detects a "regsvr32" execution where the DLL doesn't contain a common file extension.
References:
  -https://app.any.run/tasks/34221348-072d-4b70-93f3-aa71f6ebecad/
Author: Florian Roth (Nextron Systems)
Date: 2019-07-17
modified:2023-05-24
Tags:

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

Logsource:

• category: process_creation
• product: windows

Detection:
  selection:
Image|endswith:'\regsvr32.exe' OriginalFileName:'REGSVR32.EXE'   filter_main_legit_ext:
    CommandLine|contains:
      -'.ax'
      -'.cpl'
      -'.dll'
      -'.ocx'

  filter_optional_pascal:
    CommandLine|contains: '.ppl'
  filter_optional_avg:
    CommandLine|contains: '.bav'
  filter_main_null_4688:
    CommandLine: 'None'
  filter_main_empty_4688:
    CommandLine: ''
  condition:selection and not 1 of filter_main_* and not 1 of filter_optional_*
Falsepositives:
  -Other legitimate extensions currently not in the list either from third party or specific Windows components.
Level: medium