---
cve: "CVE-2026-50538"
severity: "HIGH"
cvss: 8.8
epss: "31.6%"
vendor: "LibVNC"
kev: false
exploited: false
published: "2026-08-21 21:16:59"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-08-31T16:38:01+02:00"
---

# CVE-2026-50538

> 8.8 HIGH · 🧪 PoC

## Beschreibung

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-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Erforderlich | good |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Hoch | bad |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- 9b54b1ec32731bd23158ca014dc18014db4194c3 (Commit)
- 540332be3e0acc566fa64da6f1b4680c72c724dd (Commit)

## Referenzen

- <https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8>
- <https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-50538) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_