Null Pointer Dereference Vulnerability in LibVNCServer: Denial of Service Risk
Summary
DEBIAN-CVE-2026-32854: LibVNCServer versions 0.9.15 and prior (fixed in commit dc78dee) contain null pointer dereference vulnerabilities in the HTTP proxy handlers within httpProcessInput() in httpd.c that allow remote attackers to cause a den... Affects libvncserver versions 0.9.13+dfsg-2 – 0.9.15+dfsg-2. No fix is published. How to fix ↓
Check if this vulnerability affects your application
Upload a manifest or SBOM and we'll show whether you're affected, plus every other risky package in the same scan.
No signup required · Results in about 60 seconds
Background
LibVNCServer is an open-source implementation of the Virtual Network Computing (VNC) protocol, which allows remote access to graphical desktops. It is widely used in various applications for remote desktop sharing and control. The package is known for its flexibility and ease of integration into different systems. However, certain versions of LibVNCServer have been found to contain vulnerabilities that can be exploited by attackers, particularly when the HTTP proxy features are enabled.
Vulnerability Detail
LibVNCServer versions 0.9.15 and prior are susceptible to null pointer dereference vulnerabilities in the HTTP proxy handlers, specifically within the httpProcessInput() function in httpd.c. This vulnerability arises from the lack of validation of the return values from the strchr() function in the CONNECT and GET proxy handling paths. Attackers can exploit this flaw by sending specially crafted HTTP requests, leading to a denial of service as the server crashes when these requests are processed. The impact is significant, especially for systems that rely on the HTTP proxy functionality, as it can render the service unavailable to legitimate users.
How To Fix
No fixed version is published for this vulnerability.
Tip — Not sure whether your app is affected? Vulert can check the versions your app actually runs. Scan free →
Workaround
If immediate patching is not feasible, consider disabling the HTTP proxy features in LibVNCServer to mitigate the risk of exploitation. This can be done by modifying the server configuration to turn off the HTTP proxy settings, thereby preventing attackers from sending malicious requests that could trigger the vulnerability.
Conclusion
The null pointer dereference vulnerability in LibVNCServer poses a significant risk of denial of service, particularly for systems utilizing HTTP proxy features. It is crucial to update to the latest version to protect against potential exploitation. Users should also consider disabling vulnerable features as an immediate workaround.
See every vulnerability recorded for libvncserver →
FAQ
The CVSS score of this vulnerability is 7.5, indicating a high severity level.
LibVNCServer versions 0.9.15 and prior are affected by this vulnerability.
You can use Vulert, which monitors and alerts for open-source vulnerabilities in real-time. You can check if your application is affected by this vulnerability using the Vulert playground at Vulert Scanner without any signup.
The primary consequence is a denial of service, where the server may crash, making it unavailable to legitimate users.
Yes, you can disable the HTTP proxy features in LibVNCServer as a temporary workaround to mitigate the risk.
References
Related vulnerabilities
Recent vulnerabilities recorded for libvncserver.
