Screensaver
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\, and C:\Windows\sysWOW64\ 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\) 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.
- Understand the behaviour - read the description and the Atomic Tests to see exactly what the attacker does on a host or network.
- Find the telemetry - what data source would reveal it (process creation, registry, network flow, auth logs). Detection Coverage shows which surfaces already have a rule and which are blind.
- Get or write the detection - adapt ready logic (CAR Analytics, SIEM Detections, Falco, or Sigma via Generate a SIEM detection), or author your own.
- Test it - run an Atomic Test in a lab and confirm your rule actually fires. A detection you have not tested is a hope, not coverage.
- Deploy and tune - push it, then watch for false positives and adjust.