CVE-2018-7226
📋 TL;DR
This vulnerability in LibVNC/vncterm allows remote attackers to cause integer overflow via specially crafted VNC packets due to missing length sanitization in vcSetXCutTextProc(). It affects systems running LinuxVNC or VNCommand from the LibVNC/vncterm distribution. Attackers could potentially execute arbitrary code or cause denial of service.
💻 Affected Systems
- LinuxVNC
- VNCommand
- LibVNC/vncterm
📦 What is this software?
Vncterm by Vncterm Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise
Likely Case
Denial of service (crash) or memory corruption
If Mitigated
Limited impact if network segmentation and access controls prevent VNC traffic
🎯 Exploit Status
Exploitation requires sending specially crafted VNC packets to vulnerable service
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 0.9.10
Vendor Advisory: https://github.com/LibVNC/vncterm/issues/6
Restart Required: Yes
Instructions:
1. Update to latest version from official repository 2. Recompile if using source 3. Restart VNC services
🔧 Temporary Workarounds
Network Segmentation
linuxRestrict VNC traffic to trusted networks only
iptables -A INPUT -p tcp --dport 5900:5910 -s TRUSTED_NETWORK -j ACCEPT
iptables -A INPUT -p tcp --dport 5900:5910 -j DROP
Service Disablement
linuxDisable VNC services if not required
systemctl stop vncserver
systemctl disable vncserver
🧯 If You Can't Patch
- Implement strict network access controls to limit VNC traffic
- Use application firewalls to inspect and filter VNC protocol traffic
🔍 How to Verify
Check if Vulnerable:
Check installed version: dpkg -l | grep vncterm or rpm -qa | grep vnctermCheck Version:
vncterm --version 2>/dev/null || dpkg -l | grep vncterm || rpm -qa | grep vnctermVerify Fix Applied:
Verify version is >0.9.10 and check service logs for stability📡 Detection & Monitoring
Log Indicators:
- VNC service crashes
- Memory corruption errors in system logs
- Unusual VNC connection attempts
Network Indicators:
- Malformed VNC protocol packets
- Multiple connection attempts to VNC ports
SIEM Query:
source="*vnc*" AND (error OR crash OR "segmentation fault")