---
id: CVE-2026-50538
title: LibVNCClient is a library for easy implementation of a VNC client
summary: >-
  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
  i…
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-122
  - CWE-787
published: '2026-08-21'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T19:57:08.043'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-50538'
references:
  - url: >-
      https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd
    label: security-advisories@github.com
  - url: >-
      https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8
    label: security-advisories@github.com
  - url: >-
      https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00605
epssPercentile: 0.46983
ingestedAt: '2026-09-30T20:23:19.469Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.