CVE-2026-44988: Libvnc Libvncserver

High severity, CVSS 8.8. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Libvnc Libvncserver: up to and including 0.9.15

Published 2026-05-27. Last modified 2026-06-17.