Full Report
Findings of research on different implementations of the VNC remote access system. Memory corruption vulnerabilities were found, some of which, if exploited, could lead to remote code execution.
Analysis Summary
# Vulnerability: Multiple Memory Corruption Flaws in VNC Implementations
## CVE Details
- **CVE ID:** CVE-2019-15757, CVE-2019-15758, CVE-2019-15759, CVE-2019-15760, CVE-2019-8339, CVE-2019-15678, CVE-2019-15679, CVE-2019-15680, CVE-2019-15681 (and others)
- **CVSS Score:** Range from 7.5 to 9.8 (Critical)
- **CWE:** CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), CWE-190 (Integer Overflow), CWE-787 (Out-of-bounds Write)
## Affected Systems
- **Products:** LibVNC, UltraVNC, TightVNC 1.X, TurboVNC
- **Versions:**
- **LibVNC:** Versions prior to 0.9.12
- **UltraVNC:** Versions prior to 1.2.2.4
- **TightVNC 1.X:** All versions prior to current patches (v1.3.10)
- **TurboVNC:** Versions prior to 2.2.3
- **Configurations:** Systems running VNC server or client components exposed to untrusted networks.
## Vulnerability Description
Research identified 37+ memory corruption vulnerabilities across popular VNC implementations. These flaws primarily stem from incorrect usage of heap memory and integer overflows during data processing. Specifically, vulnerabilities were found in how VNC clients process screen updates and pixel data sent from a server, as well as how servers handle client authentication and connection handshake packets.
## Exploitation
- **Status:** PoC available (developed by researchers); no widespread exploitation in the wild at the time of publication.
- **Complexity:** Medium
- **Attack Vector:** Network (Remote) – An attacker can exploit these either by hosting a malicious VNC server and tricking a client to connect, or by sending specially crafted packets to a vulnerable VNC server.
## Impact
- **Confidentiality:** High (Potential for Remote Code Execution/Information Disclosure)
- **Integrity:** High (Unauthorized system modification)
- **Availability:** High (Service crashes/DoS)
## Remediation
### Patches
- **LibVNC:** Update to version 0.9.12 or later.
- **UltraVNC:** Update to version 1.2.2.4 or later.
- **TurboVNC:** Update to version 2.2.3 or later.
- **TightVNC:** TightVNC 1.X is no longer officially supported for security updates; users are encouraged to move to version 2.X or apply community patches.
### Workarounds
- Implement strong authentication and use SSH tunneling or VPNs to encrypt VNC traffic.
- Restrict VNC access to trusted IP addresses only.
- Disable VNC services if not explicitly required for business operations.
## Detection
- **Indicators of compromise:** Unusual network traffic patterns on port 5900 (or other configured VNC ports); unexpected crashes of VNC service processes (`winvnc.exe`, `vncserver`).
- **Detection methods and tools:** Use network IDS/IPS signatures to monitor for malformed VNC RFB (Remote Framebuffer) protocol packets. Periodically scan for vulnerable versions using vulnerability scanners (Nessus, OpenVAS).
## References
- **Vendor advisories:**
- LibVNC Security: hxxps[://]github[.]com/LibVNC/libvncserver/releases
- UltraVNC Updates: hxxp[://]www[.]uvnc[.]com/downloads/ultravnc.html
- **Relevant links:**
- Kaspersky ICS CERT Report: hxxps[://]ics-cert[.]kaspersky[.]com/publications/reports/2019/11/22/vnc-vulnerability-research/
- CVE Database: hxxps[://]cve[.]mitre[.]org/cgi-bin/cvename[.]cgi?name=CVE-2019-15678