# CVE-2026-50538: libvncserver: LibVNCClient is a library for easy implementation of a VNC client

CVE-2026-50538 is fixed in 4 products on 1 platform, first by libvncclient1 0.9.15+dfsg-3ubuntu0.2, released June 14, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-50538
- Priority: High
- CVSS: 8.8 (high)
- EPSS: 0.0040
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 14, 2026

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | LibVNCServer opensuse-leap 16.0 | 0.9.14-160000.6.1 | [OPENSUSE-SU-2026:21735-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21735-1.md) | Sep 2, 2026 |
| Linux | LibVNCServer sles 15.7 | 0.9.14-150600.3.12.1 | [SUSE-SU-2026:4022-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-4022-1.md) | Sep 7, 2026 |
| Linux | LibVNCServer sles 16.0 | 0.9.14-160000.6.1 | [SUSE-SU-2026:23601-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23601-1.md) | Sep 2, 2026 |
| Linux | libvncclient1 Ubuntu 22.04.1 LTS (jammy) | 0.9.13+dfsg-3ubuntu0.2 | [libvncclient1 0.9.13+dfsg-3ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libvncclient1-0.9.13-dfsg-3ubuntu0.2.md) | Jul 3, 2026 |
| Linux | libvncclient1 Ubuntu 24.04.5 LTS (noble) | 0.9.14+dfsg-1ubuntu0.2 | [libvncclient1 0.9.14+dfsg-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libvncclient1-0.9.14-dfsg-1ubuntu0.2.md) | Jul 3, 2026 |
| Linux | libvncclient1 Ubuntu 25.10 (questing) | 0.9.15+dfsg-1ubuntu0.2 | [libvncclient1 0.9.15+dfsg-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-questing-libvncclient1-0.9.15-dfsg-1ubuntu0.2.md) | Jul 3, 2026 |
| Linux | libvncclient1 Ubuntu 26.04.1 LTS (resolute) | 0.9.15+dfsg-3ubuntu0.2 | [libvncclient1 0.9.15+dfsg-3ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libvncclient1-0.9.15-dfsg-3ubuntu0.2.md) | Jun 14, 2026 |
| Linux | libvncserver Debian 12.15 (bookworm) | 0.9.14+dfsg-1+deb12u2 | [DEBIAN-CVE-2026-50538](https://patchblox.com/security/data/fix/linux/debian-cve-2026-50538.md) | Jun 24, 2026 |
| Linux | libvncserver Debian 13.5 (trixie) | 0.9.15+dfsg-1+deb13u2 | [DEBIAN-CVE-2026-50538](https://patchblox.com/security/data/fix/linux/debian-cve-2026-50538.md) | Jun 24, 2026 |
| Linux | libvncserver Debian 14 | 0.9.15+dfsg-6 | [DEBIAN-CVE-2026-50538](https://patchblox.com/security/data/fix/linux/debian-cve-2026-50538.md) | Jun 24, 2026 |
| Linux | libvncserver1 Ubuntu 22.04.1 LTS (jammy) | 0.9.13+dfsg-3ubuntu0.2 | [libvncserver1 0.9.13+dfsg-3ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libvncserver1-0.9.13-dfsg-3ubuntu0.2.md) | Jul 3, 2026 |
| Linux | libvncserver1 Ubuntu 24.04.5 LTS (noble) | 0.9.14+dfsg-1ubuntu0.2 | [libvncserver1 0.9.14+dfsg-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libvncserver1-0.9.14-dfsg-1ubuntu0.2.md) | Jul 3, 2026 |
| Linux | libvncserver1 Ubuntu 25.10 (questing) | 0.9.15+dfsg-1ubuntu0.2 | [libvncserver1 0.9.15+dfsg-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-questing-libvncserver1-0.9.15-dfsg-1ubuntu0.2.md) | Jul 3, 2026 |
| Linux | libvncserver1 Ubuntu 26.04.1 LTS (resolute) | 0.9.15+dfsg-3ubuntu0.2 | [libvncserver1 0.9.15+dfsg-3ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libvncserver1-0.9.15-dfsg-3ubuntu0.2.md) | Jun 14, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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