CVE-2011-2187
📋 TL;DR
This vulnerability in xscreensaver before version 5.14 causes the screensaver to crash during activation when configured in 'Blank Only Mode' with DPMS disabled. This leaves the screen unlocked, allowing local attackers to bypass authentication and access the user's session. Systems using xscreensaver with these specific configurations are affected.
💻 Affected Systems
- xscreensaver
📦 What is this software?
Xscreensaver by Xscreensaver Project
⚠️ Risk & Real-World Impact
Worst Case
Local attacker gains full access to logged-in user's session, potentially accessing sensitive data, executing commands, or escalating privileges.
Likely Case
Local attacker bypasses screensaver lock to access an unattended workstation, viewing or modifying user data.
If Mitigated
With proper physical security controls, risk is limited to authorized personnel who could already access the system physically.
🎯 Exploit Status
Exploitation requires local access to trigger the screensaver crash. The vulnerability details and reproduction steps are publicly documented in bug reports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.14 and later
Vendor Advisory: https://www.jwz.org/xscreensaver/changelog.html
Restart Required: No
Instructions:
1. Update xscreensaver to version 5.14 or later using your distribution's package manager. 2. For Debian/Ubuntu: sudo apt-get update && sudo apt-get install xscreensaver. 3. For RHEL/CentOS: Use yum update xscreensaver. 4. Verify installation with xscreensaver -version.
🔧 Temporary Workarounds
Enable DPMS
linuxEnable DPMS (Display Power Management Signaling) in xscreensaver configuration to prevent the vulnerable condition.
xscreensaver-demo
Then navigate to Advanced tab and ensure 'Enable DPMS' is checked
Disable Blank Only Mode
linuxChange screensaver mode from 'Blank Only' to any other mode that doesn't trigger the crash.
xscreensaver-demo
Select a different screensaver mode from the main tab
🧯 If You Can't Patch
- Ensure DPMS is enabled in xscreensaver configuration
- Disable 'Blank Only Mode' and use a different screensaver mode
- Implement strict physical security controls for workstations
- Configure automatic logout after inactivity at OS level
🔍 How to Verify
Check if Vulnerable:
Check xscreensaver version with 'xscreensaver -version' and verify if below 5.14. Also check configuration: run 'xscreensaver-demo' and verify if 'Blank Only' mode is selected AND DPMS is disabled.Check Version:
xscreensaver -versionVerify Fix Applied:
After update, run 'xscreensaver -version' to confirm version 5.14 or higher. Test screensaver activation with Blank Only mode and DPMS disabled to ensure it no longer crashes.📡 Detection & Monitoring
Log Indicators:
- xscreensaver crash logs in system logs
- Unexpected screensaver deactivation events
- Multiple failed lock attempts followed by successful access
Network Indicators:
- None - this is a local attack
SIEM Query:
process:xscreensaver AND event:crash OR screensaver:deactivated AND user:session_unlocked🔗 References
- https://access.redhat.com/security/cve/cve-2011-2187
- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=627382
- https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2011-2187
- https://security-tracker.debian.org/tracker/CVE-2011-2187
- https://www.jwz.org/xscreensaver/changelog.html
- https://www.openwall.com/lists/oss-security/2011/06/06/17
- https://access.redhat.com/security/cve/cve-2011-2187
- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=627382
- https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2011-2187
- https://security-tracker.debian.org/tracker/CVE-2011-2187
- https://www.jwz.org/xscreensaver/changelog.html
- https://www.openwall.com/lists/oss-security/2011/06/06/17
