TL;DR
Allowing users to change wallpapers and screensavers can introduce cyber security risks, but these are usually low if managed correctly. The main concern is malicious images embedding code or the use of network locations for wallpaper storage. We’ll cover how to minimise those risks.
Solution Guide
- Understand the Risks
- Malicious Images: A carefully crafted image file (JPEG, PNG, etc.) could contain hidden code that executes when the wallpaper is applied. This is rare but possible.
- Network Shares: If users can set wallpapers from network shares, those shares become a potential attack vector. If the share has weak permissions, an attacker could replace legitimate wallpapers with malicious ones.
- Group Policy Exploitation (Less Common): In some cases, vulnerabilities in Group Policy processing related to wallpaper settings have been exploited. Keeping systems patched is vital.
Group Policy is the best way to control this centrally on a Windows domain.
- Wallpaper Control: Use the ‘Prevent users from changing desktop background’ setting under User Configuration > Administrative Templates > Desktop. Set this to ‘Enabled’ if you want to completely prevent changes, or leave it ‘Not Configured’ or ‘Disabled’ for controlled allowance.
- Screen Saver Control: Use the ‘Prevent users from changing screen saver settings’ setting under User Configuration > Administrative Templates > Control Panel > Screen Saver. Similar options apply here – enable to prevent changes, disable/not configure to allow them.
- Wallpaper Source Restriction (Important): This is key! Under User Configuration > Administrative Templates > Desktop, use the ‘Specify wallpaper’ setting. Configure this to point to a local folder containing approved wallpapers only.
Computer ConfigurationAdministrative TemplatesDesktopDesktop Specify wallpaper: %SystemRoot%WindowsWebWallpaperThemes
- Local Folder: As mentioned above, store approved wallpapers in a local folder (e.g.,
C:WindowsWebWallpaperThemes). This avoids network share risks. - Permissions: If you *must* use a network share for wallpapers:
- Restrict write access to only the necessary accounts (usually an administrator account used for deployment). Users should have read-only access.
- Regularly audit the share’s contents for unexpected files.
- Scan Images: Before adding any wallpaper to your approved folder, scan it with up-to-date anti-virus software.
- File Type Restrictions (Optional): Consider restricting allowed file types to common image formats like JPG, PNG, and BMP. This can be done via Group Policy using Software Restriction Policies or AppLocker (more advanced).
- Event Logs: Monitor the Windows Event Logs for suspicious activity related to wallpaper changes. Look for events in the Security log that might indicate unauthorized modifications.
Event ID 4657 (A registry value was modified) - look for changes to keys under HKEY_CURRENT_USERControl PanelDesktop - Regular Audits: Periodically review Group Policy settings and wallpaper storage locations.
Ensure all Windows systems are patched with the latest security updates to mitigate potential vulnerabilities in Group Policy processing or image handling.