CVE-2026-44988
LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes
Description
LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient's Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1.
INFO
Published Date :
May 27, 2026, 3:16 p.m.
Last Modified :
Oct. 26, 2026, 11:10 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-44988
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update LibVNCClient to version post-commit 5b270544b85233668b98161323297d418a8f5fd1.
- Verify that the Tight encoding decoder handles rectangle widths correctly.
- Apply security patches for all LibVNCClient-based applications.
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-2026-44988.
| URL | Resource |
|---|---|
| https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1 | |
| https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-44988 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-2026-44988
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-2026-44988 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-44988 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.
-
CVE Translated by [email protected]
Oct. 26, 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 0.9.15 y versiones anteriores, el decodificador de codificación Tight de LibVNCClient utiliza búferes temporales de tamaño fijo de 2048 píxeles para el filtro Gradient, pero no rechaza los rectángulos Tight cuyo ancho es mayor de 2048 píxeles. Un servidor VNC malicioso puede enviar un rectángulo FramebufferUpdate manipulado utilizando codificación Tight con NoZlib | ExplicitFilter y el filtro Gradient. Cuando un cliente basado en LibVNCClient se conecta, el cliente procesa el ancho del rectángulo controlado por el servidor y escribe más allá de los búferes Gradient de tamaño fijo. Esta vulnerabilidad se corrige con el commit 5b270544b85233668b98161323297d418a8f5fd1. -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'LibVNC', 'product': 'libvncserver', 'versions': [{'status': 'affected', 'version': '<= 0.9.15'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-44988', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-05-29T03:55:55.774539Z'} -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
May. 29, 2026
Action Type Old Value New Value Removed Reference https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58 -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
May. 28, 2026
Action Type Old Value New Value Added Reference https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58 -
New CVE Received by [email protected]
May. 27, 2026
Action Type Old Value New Value Added Description LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient's Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1. 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 Reference https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1 Added Reference https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58