CVE-2026-44988 LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes
A malicious VNC server can trigger out-of-bounds writes in LibVNCClient via crafted Tight encoding rectangles, potentially leading to code execution on the client.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-44988?
CVE-2026-44988 is a high-severity memory corruption vulnerability in libvncserver, published on 27 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-787
Which versions are affected by CVE-2026-44988?
Linux distribution packages (8)
LibVNCServer SUSE:Linux Enterprise Module for Package Hub 15 SP7 | All versions | 0.9.14-150600.3.9.1 |
LibVNCServer SUSE:Linux Enterprise Server 12 SP5-LTSS | All versions | 0.9.9-17.47.1 |
LibVNCServer SUSE:Linux Enterprise Server 16.0 | All versions | 0.9.14-160000.5.1 |
LibVNCServer SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | All versions | 0.9.9-17.47.1 |
LibVNCServer SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 0.9.14-160000.5.1 |
LibVNCServer SUSE:Linux Enterprise Workstation Extension 15 SP7 | All versions | 0.9.14-150600.3.9.1 |
LibVNCServer openSUSE:Leap 16.0 | All versions | 0.9.14-160000.5.1 |
LibVNCServer openSUSE:Tumbleweed | All versions | 0.9.15-3.1 |
How do I fix CVE-2026-44988?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-44988 being exploited?
There is no known exploitation of CVE-2026-44988 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-44988, GHSA-jcc5-8wj4-7c58, OESA-2026-2490, OESA-2026-2491, OESA-2026-2564, OESA-2026-2565 and 7 more.