Heap-based Buffer Overflow Affecting libvncserver package, versions <0.9.13+dfsg-3ubuntu0.2


Severity

Recommended
medium

Based on Ubuntu security rating.

Threat Intelligence

EPSS
0.4% (33rd percentile)

Do your applications use this vulnerable package?

In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.

Test your applications
  • Snyk IDSNYK-UBUNTU2204-LIBVNCSERVER-17340445
  • published2 Jul 2026
  • disclosed21 Aug 2026

Introduced: 2 Jul 2026

CVE-2026-50538  (opens in a new tab)
CWE-122  (opens in a new tab)
CWE-787  (opens in a new tab)

How to fix?

Upgrade Ubuntu:22.04 libvncserver to version 0.9.13+dfsg-3ubuntu0.2 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream libvncserver package and not the libvncserver package as distributed by Ubuntu. See How to fix? for Ubuntu:22.04 relevant fixed versions and status.

LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, a malicious (or man-in-the-middle) VNC server can force a connecting libvncclient to write attacker-controlled data past the end of its framebuffer. This is an out-of-bounds heap write with attacker-controlled length, contents, and offset. It needs no authentication (the attacker is the server), works in a default build with default settings, and fires from a single FramebufferUpdate the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue.

CVSS Base Scores

version 3.1