CVE-2026-50538
libvncclient Tight decoder has an attacker-controlled heap out-of-bounds write
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.
INFO
Published Date :
Aug. 21, 2026, 9:16 p.m.
Last Modified :
Oct. 12, 2026, 4:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Update LibVNCClient to version 0.9.16 or later.
- Apply commit 540332be3e0acc566fa64da6f1b4680c72c724dd.
- Rebuild the application with the patched library.
- Restart the application after updating.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-50538.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-50538 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-50538
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-50538 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-50538 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Translated by [email protected]
Oct. 12, 2026
Action Type Old Value New Value Added Translation Title: libvncserver de LibVNC, Description: LibVNCClient es una biblioteca para la fácil implementación de un cliente VNC. En las versiones 0.9.12 a la 0.9.15, un servidor VNC malicioso (o man-in-the-middle) puede forzar a un 'libvncclient' que se conecta a escribir datos controlados por el atacante más allá del final de su framebuffer. Esto es una escritura de heap fuera de límites con longitud, contenido y desplazamiento controlados por el atacante. No necesita autenticación (el atacante es el servidor), funciona en una compilación predeterminada con configuraciones predeterminadas, y se activa desde una única 'FramebufferUpdate' en el momento en que la víctima se conecta. Bloquea cualquier cliente incondicionalmente (denegación de servicio); también demostramos que sobrescribe un puntero de callback de aplicación y redirige la ejecución a código elegido por el atacante (ejecución de código) bajo la configuración predeterminada. El commit 540332be3e0acc566fa64da6f1b4680c72c724dd corrige el problema. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 24, 2026
Action Type Old Value New Value Added Reference https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8 Added SSVC {'id': 'CVE-2026-50538', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-08-24T19:39:31.246844Z'} -
New CVE Received by [email protected]
Aug. 21, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'LibVNC', 'product': 'libvncserver', 'versions': [{'status': 'affected', 'version': '>= 0.9.12, <= 0.9.15'}]}] Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Added CWE CWE-787 Added CWE CWE-122 Added Reference https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd Added Reference https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8