CVE-2019-17624
📋 TL;DR
CVE-2019-17624 is a stack-based buffer overflow vulnerability in X.Org X Server's XQueryKeymap function. Attackers can trigger this by sending excessive data, potentially causing denial of service (crash) or arbitrary code execution. This affects systems running vulnerable versions of X.Org X Server, primarily Linux/Unix systems with graphical interfaces.
💻 Affected Systems
- X.Org X Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full system compromise if combined with other vulnerabilities, though this is disputed and less likely.
Likely Case
Local denial of service (application crash) requiring attacker access to the X server session.
If Mitigated
Minimal impact if proper access controls limit local user privileges and X server exposure.
🎯 Exploit Status
Exploit requires local access to the X server. Proof-of-concept code is publicly available showing denial of service. Code execution potential is disputed and unconfirmed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check X.Org releases for updates beyond 1.20.4
Vendor Advisory: https://www.x.org/releases/individual/xserver/
Restart Required: Yes
Instructions:
1. Check current X server version. 2. Update through your distribution's package manager (apt, yum, etc.). 3. Restart the X server or reboot the system.
🔧 Temporary Workarounds
Restrict X Server Access
linuxLimit which users can connect to the X server display to reduce attack surface
xhost -
xhost +si:localuser:username (allow specific users only)
Use X11 Forwarding Restrictions
linuxDisable or restrict X11 forwarding in SSH configurations
Set 'X11Forwarding no' in /etc/ssh/sshd_config
🧯 If You Can't Patch
- Implement strict access controls on X server displays using xhost or xauth
- Isolate systems with vulnerable X servers from untrusted networks and users
🔍 How to Verify
Check if Vulnerable:
Check X server version: Xorg -version or check package version via distribution package managerCheck Version:
Xorg -version 2>/dev/null | grep -i 'x.org x server' || dpkg -l | grep -i xserver-xorg-core || rpm -qa | grep -i xorg-x11-serverVerify Fix Applied:
Verify updated version is installed and test X server functionality remains intact📡 Detection & Monitoring
Log Indicators:
- X server crash logs in /var/log/Xorg.*.log
- Abnormal termination of X server processes
Network Indicators:
- Unusual X protocol traffic patterns to display sockets
SIEM Query:
process:name="Xorg" AND event:action="terminated" OR log_source:"/var/log/Xorg.*.log" AND message:"segmentation fault" OR "buffer overflow"🔗 References
- http://packetstormsecurity.com/files/154868/X.Org-X-Server-1.20.4-Local-Stack-Overflow.html
- https://www.exploit-db.com/exploits/47507
- https://www.x.org/releases/individual/xserver/
- http://packetstormsecurity.com/files/154868/X.Org-X-Server-1.20.4-Local-Stack-Overflow.html
- https://www.exploit-db.com/exploits/47507
- https://www.x.org/releases/individual/xserver/
