CVE-2019-15690
📋 TL;DR
CVE-2019-15690 is a heap buffer overflow vulnerability in LibVNCServer that allows remote attackers to execute arbitrary code by sending specially crafted cursor shapes. This affects all systems running LibVNCServer version 0.9.12 and earlier. The vulnerability is exploitable over the network without authentication.
💻 Affected Systems
- LibVNCServer
- Any software using LibVNCServer library
- VNC server implementations based on LibVNCServer
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with full system compromise, allowing attacker to install malware, exfiltrate data, or pivot to other systems.
Likely Case
Remote code execution leading to system compromise, data theft, or ransomware deployment.
If Mitigated
Denial of service or system crash if exploit fails, but proper patching prevents exploitation entirely.
🎯 Exploit Status
Exploitation requires sending specially crafted cursor shape packets to trigger the heap overflow.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: LibVNCServer 0.9.13 and later
Vendor Advisory: https://github.com/LibVNC/libvncserver/releases/tag/LibVNCServer-0.9.13
Restart Required: Yes
Instructions:
1. Download LibVNCServer 0.9.13 or later from official repository. 2. Compile and install the updated library. 3. Recompile any applications using LibVNCServer. 4. Restart affected VNC services.
🔧 Temporary Workarounds
Network Segmentation
allRestrict VNC server access to trusted networks only using firewall rules.
Disable Cursor Shape Support
allIf possible, disable cursor shape handling in VNC server configuration.
🧯 If You Can't Patch
- Implement strict network access controls to limit VNC server exposure
- Monitor for unusual network traffic patterns to/from VNC servers
🔍 How to Verify
Check if Vulnerable:
Check LibVNCServer version with: ldd --version | grep -i vnc or check package manager for installed version.Check Version:
vncserver --version 2>&1 | grep -i libvnc || ldd $(which vncserver) 2>/dev/null | grep -i libvncVerify Fix Applied:
Verify version is 0.9.13 or higher using same version check command.📡 Detection & Monitoring
Log Indicators:
- Unusual cursor shape requests in VNC logs
- Memory allocation errors in system logs
- Process crashes of VNC server
Network Indicators:
- Unusual cursor shape packets to VNC port (typically 5900+)
- Large or malformed RFB protocol packets
SIEM Query:
source_port=5900+ AND (payload_contains="cursor" OR packet_size>threshold)