Windows Registry COM Hijacking via scrobj.dll InprocServer32(Default) Persistence

Alerts on registry modifications setting InprocServer32(Default) to scrobj.dll, indicating possible COM hijacking persistence.

FreeUnreviewedSigmamediumv1

windows-registry-com-hijacking-via-scrobj-dll-inprocserver32-default-persistence-fe20dda1

title: Windows Registry COM Hijacking via scrobj.dll InprocServer32(Default) Persistence
id: ae7930bc-087a-4807-a8d0-b91bbac10ab7
status: test
description: This rule flags registry changes where the COM in-proc server for the default value is set to C:\WINDOWS\system32\scrobj.dll under an InprocServer32\(Default) target. COM Hijacking is a common persistence technique because it can redirect how Windows loads and instantiates COM components. The detection relies on registry set telemetry that captures the TargetObject ending pattern and the specific Details value pointing to scrobj.dll.
references:
  - https://github.com/redcanaryco/atomic-red-team/blob/40b77d63808dd4f4eafb83949805636735a1fd15/atomics/T1546.015/T1546.015.md
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_set/registry_set_persistence_scrobj_dll.yml
author: frack113, Huntrule Team
date: 2022-08-20
modified: 2023-08-17
tags:
  - attack.privilege-escalation
  - attack.persistence
  - attack.t1546.015
logsource:
  category: registry_set
  product: windows
detection:
  selection:
    TargetObject|endswith: InprocServer32\(Default)
    Details: C:\WINDOWS\system32\scrobj.dll
  condition: selection
falsepositives:
  - Legitimate use of the dll.
level: medium
license: DRL-1.1
related:
  - id: fe20dda1-6f37-4379-bbe0-a98d400cae90
    type: derived

What it detects

This rule flags registry changes where the COM in-proc server for the default value is set to C:\WINDOWS\system32\scrobj.dll under an InprocServer32\(Default) target. COM Hijacking is a common persistence technique because it can redirect how Windows loads and instantiates COM components. The detection relies on registry set telemetry that captures the TargetObject ending pattern and the specific Details value pointing to scrobj.dll.

Known false positives

Legitimate use of the dll.

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.