Detectionmediumtest

Suspicious ScreenSave Change by Reg.exe

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

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Open this Sigma rule in the converter with the YAML preloaded and ready for backend selection.

Launch

François HubautCreated Thu Aug 19Updated Thu Jun 020fc35fc3-efe6-4898-8a37-0b233339524fwindows

Log Source

WindowsProcess Creation

ProductWindows← raw: windows

CategoryProcess Creation← raw: process_creation

Events generated when a new process is spawned on the system. Covers command-line arguments, parent/child relationships, and process metadata.

Detection Logic

detection:
    selection_reg:
        Image|endswith: '\reg.exe'
        CommandLine|contains:
            - 'HKEY_CURRENT_USER\Control Panel\Desktop'
            - 'HKCU\Control Panel\Desktop'
    selection_option_1: # /force Active ScreenSaveActive
        CommandLine|contains|all:
            - '/v ScreenSaveActive'
            - '/t REG_SZ'
            - '/d 1'
            - '/f'
    selection_option_2: # /force  set ScreenSaveTimeout
        CommandLine|contains|all:
            - '/v ScreenSaveTimeout'
            - '/t REG_SZ'
            - '/d '
            - '/f'
    selection_option_3: # /force set ScreenSaverIsSecure
        CommandLine|contains|all:
            - '/v ScreenSaverIsSecure'
            - '/t REG_SZ'
            - '/d 0'
            - '/f'
    selection_option_4: # /force set a .scr
        CommandLine|contains|all:
            - '/v SCRNSAVE.EXE'
            - '/t REG_SZ'
            - '/d '
            - '.scr'
            - '/f'
    condition: selection_reg and 1 of selection_option_*