Windows Registry Screensaver Path Value Modified (SCRNSAVE.EXE)

title: Windows Registry Screensaver Path Value Modified (SCRNSAVE.EXE)
id: a9759478-0ca8-4d2b-ab0f-0863e6867132
status: test
description: This rule flags modifications to a Windows registry value that contains the configured screensaver binary path for HKEY_CURRENT_USER\Control Panel\Desktop\SCRNSAVE.EXE. Attackers can abuse screensaver execution to persist by redirecting the screensaver binary to attacker-controlled code. The detection relies on registry event telemetry matching the TargetObject ending in the SCRNSAVE.EXE registry path while excluding changes attributed to certain Image processes.
references:
  - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1546.002/T1546.002.md
  - https://www.welivesecurity.com/wp-content/uploads/2017/08/eset-gazer.pdf
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_event/registry_event_modify_screensaver_binary_path.yml
author: Bartlomiej Czyz @bczyz1, oscd.community, Huntrule Team
date: 2020-10-11
modified: 2021-11-27
tags:
  - attack.persistence
  - attack.privilege-escalation
  - attack.t1546.002
logsource:
  category: registry_event
  product: windows
detection:
  selection:
    TargetObject|endswith: \Control Panel\Desktop\SCRNSAVE.EXE
  filter:
    Image|endswith:
      - \rundll32.exe
      - \explorer.exe
  condition: selection and not filter
falsepositives:
  - Legitimate modification of screensaver
level: medium
license: DRL-1.1
related:
  - id: 67a6c006-3fbe-46a7-9074-2ba3b82c3000
    type: derived