Detect Screensaver in CrowdStrike LogScale
Adversaries may establish persistence by modifying the Windows screensaver configuration. Screensavers are programs that execute after a configurable time of user inactivity and consist of Portable Executable (PE) files with a .scr file extension. Adversaries can abuse this by modifying the SCRNSAVE.EXE registry value in HKCU\Control Panel\Desktop to point to a malicious executable that runs whenever the screen saver activates.
MITRE ATT&CK
- Tactic
- Privilege Escalation Persistence
- Technique
- T1546 Event Triggered Execution
- Sub-technique
- T1546.002 Screensaver
- Canonical reference
- https://attack.mitre.org/techniques/T1546/002/
LogScale Detection Query
#event_simpleName=RegSetValue
| TargetObjectName = /Control Panel\\Desktop/i
| TargetObjectName = /SCRNSAVE\.EXE|ScreenSaveActive|ScreenSaverIsSecure|ScreenSaveTimeOut/i
| IsScrnsaveExe := TargetObjectName = /SCRNSAVE\.EXE/i
| SuspiciousValue := TargetObjectValue = /(?i)(appdata|\\temp\\|programdata|\\public\\|powershell|cmd\.exe|wscript|cscript|rundll32)/
| NotSystemPath := IsScrnsaveExe == true AND TargetObjectValue != "" AND NOT TargetObjectValue = /(?i)c:\\windows\\(system32|syswow64)\\/
| SuspiciousValue == true OR NotSystemPath == true
| select([timestamp, ComputerName, UserName, TargetObjectName, TargetObjectValue, ImageFileName, CommandLine, IsScrnsaveExe, SuspiciousValue, NotSystemPath])
| sort(field=timestamp, order=desc)CrowdStrike LogScale CQL detection for T1546.002 screensaver persistence using Falcon RegSetValue telemetry. Identifies adversarial modification of HKCU\Control Panel\Desktop screensaver registry values where SCRNSAVE.EXE is redirected to a non-system path or where registry data includes suspicious process names or staging directory paths.
Data Sources
Required Tables
False Positives & Tuning
- Falcon-visible GPO or Intune policy applications that write screensaver settings from SYSTEM or domain controller context, which may reference policy staging locations
- Help desk or IT tools using remote registry modification APIs to standardize screensaver lock policies across the fleet
- Software installers that bundle a screensaver component and register it from a non-system32 application directory during setup
Other platforms for T1546.002
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Set Malicious Screensaver Path in Registry
Expected signal: Sysmon Event ID 13 (Registry Value Set) for HKCU\Control Panel\Desktop\SCRNSAVE.EXE with Details=C:\Windows\System32\cmd.exe. Additional Event ID 13 records for ScreenSaveActive and ScreenSaveTimeOut. Security Event ID 4657 if registry auditing is enabled.
- Test 2Disable Screensaver Lock Screen for Silent Execution
Expected signal: Sysmon Event ID 13: TargetObject HKCU\Control Panel\Desktop\ScreenSaverIsSecure, Details=0. This should be correlated with concurrent SCRNSAVE.EXE changes.
- Test 3Deploy Fake Screensaver via AppData
Expected signal: Sysmon Event ID 11 (File Created): malicious.scr in AppData path. Sysmon Event ID 13: SCRNSAVE.EXE value set to AppData path. Both the file creation and registry modification events fire. The AppData path in the registry value is the primary detection trigger.
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