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Vulnerability record · CVE-2026-44988 · published 27 May 2026

CVE-2026-44988: Out-of-bounds write vulnerability

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.

8.8 CVSS 3.1 High EPSS 0.44% · top 64.1% CWE-787 · Out-of-bounds write Awaiting Analysis
8.8CVSS 3.1 base score
0.44%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

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.

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

References

LinkTags
https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1
https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58

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Source: NIST National Vulnerability Database (record CVE-2026-44988), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.