ScreenSaver Registry Key Set

Hunt Hypothesis

Detects registry key established after masqueraded .scr file execution using Rundll32 through desk.cpl

Detection Rule

Sigma (Original)

title: ScreenSaver Registry Key Set
id: 40b6e656-4e11-4c0c-8772-c1cc6dae34ce
status: test
description: Detects registry key established after masqueraded .scr file execution using Rundll32 through desk.cpl
references:
    - https://twitter.com/VakninHai/status/1517027824984547329
    - https://twitter.com/pabraeken/status/998627081360695297
    - https://jstnk9.github.io/jstnk9/research/InstallScreenSaver-SCR-files
author: Jose Luis Sanchez Martinez (@Joseliyo_Jstnk)
date: 2022-05-04
modified: 2023-08-17
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    product: windows
    category: registry_set
detection:
    selection:
        Image|endswith: '\rundll32.exe'
    registry:
        TargetObject|contains: '\Control Panel\Desktop\SCRNSAVE.EXE'
        Details|endswith: '.scr'
    filter:
        Details|contains:
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
    condition: selection and registry and not filter
falsepositives:
    - Legitimate use of screen saver
level: medium

KQL (Azure Sentinel)

imRegistry
| where ActingProcessName endswith "\\rundll32.exe" and (RegistryKey contains "\\Control Panel\\Desktop\\SCRNSAVE.EXE" and RegistryValueData endswith ".scr") and (not((RegistryValueData contains "C:\\Windows\\System32\\" or RegistryValueData contains "C:\\Windows\\SysWOW64\\")))

Required Data Sources

False Positive Guidance

• Legitimate use of screen saver

MITRE ATT&CK Context

• Technique: T1218.011 — T1218.011

References

• https://twitter.com/VakninHai/status/1517027824984547329
• https://twitter.com/pabraeken/status/998627081360695297
• https://jstnk9.github.io/jstnk9/research/InstallScreenSaver-SCR-files
• SigmaHQ Rule