cyberstrikeus T1546.002 Screensaver
Sub-technique of: T1546
High-Level Description
Adversaries may establish persistence by executing malicious content triggered by user inactivity. Screensavers are programs that execute after a configurable time of user inactivity and consist of Portable Executable (PE) files with a .scr file extension. The Windows screensaver application scrnsave.scr is located in C:\Windows\System32</code>, and C:\Windows\sysWOW64</code> on 64-bit Windows systems, along with screensavers included with base Windows installations.
The following screensaver settings are stored in the Registry (HKCU\Control Panel\Desktop</code>) and could be manipulated to achieve persistence:
- SCRNSAVE.exe - set to malicious PE path
- ScreenSaveActive - set to '1' to enable the screensaver
- ScreenSaverIsSecure - set to '0' to not require a password to unlock
- ScreenSaveTimeout - sets user inactivity timeout before screensaver is executed
Adversaries can use screensaver settings to maintain persistence by setting the screensaver to run malware after a certain timeframe of user inactivity.
Kill Chain Phase
- Privilege Escalation (TA0004)
- Persistence (TA0003)
Platforms: Windows
What to Check
- Identify if Screensaver technique is applicable to target environment
- Check Windows systems for indicators of Screensaver
- Verify mitigations are bypassed or absent (2 known mitigations)
- Assess detection coverage (1 detection strategies)
How to Test
Atomic Red Team Tests
The following tests are from Atomic Red Team and provide actionable ways to test this technique:
Atomic Test 1: Set Arbitrary Binary as Screensaver
This test copies a binary into the Windows System32 folder and sets it as the screensaver so it will execute for persistence. Requires a reboot and logon.
Supported Platforms: windows Elevation Required: Yes
reg export "HKEY_CURRENT_USER\Control Panel\Desktop" %userprofile%\backup.reg
copy #{input_binary} "%SystemRoot%\System32\evilscreensaver.scr"
reg.exe add "HKEY_CURRENT_USER\Control Panel\Desktop" /v ScreenSaveActive /t REG_SZ /d 1 /f
reg.exe add "HKEY_CURRENT_USER\Control Panel\Desktop" /v ScreenSaveTimeout /t REG_SZ /d 60 /f
reg.exe add "HKEY_CURRENT_USER\Control Panel\Desktop" /v ScreenSaverIsSecure /t REG_SZ /d 0 /f
reg.exe add "HKEY_CURRENT_USER\Control Panel\Desktop" /v SCRNSAVE.EXE /t REG_SZ /d "%SystemRoot%\System32\evilscreensaver.scr" /f
if #{reboot} NEQ 0 shutdown /r /t 0
Manual Testing
If Atomic Red Team tests are not applicable, manually verify the technique by:
Identify Attack Surface: Determine if the target environment is susceptible to Screensaver by examining the target platforms (Windows).
Assess Existing Defenses: Review whether mitigations for T1546.002 are in place. If defenses are absent or misconfigured, this technique may be exploitable.
Execute Test: Use tools and methods described in the MITRE ATT&CK page and external references below.
Remediation Guide
M1038 Execution Prevention
Block .scr files from being executed from non-standard locations.
M1042 Disable or Remove Feature or Program
Use Group Policy to disable screensavers if they are unnecessary.
Detection
Detect Screensaver-Based Persistence via Registry and Execution Chains
Risk Assessment
| Finding | Severity | Impact |
|---|---|---|
| Screensaver technique applicable | Low | Privilege Escalation |
CWE Categories
| CWE ID | Title |
|---|---|
| CWE-269 | Improper Privilege Management |