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Fencer Vulns
high 8.8

CVE-2026-44988 json

LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes

published 2026-05-27 5 mo ago modified 2026-10-26 14 d ago also EUVD-2026-32525

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits
0
none known

Summary

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.

Patch / fix

  • libvncserver Debian 12 0.9.14+dfsg-1+deb12u2
  • libvncserver Debian 13 0.9.15+dfsg-1+deb13u2
  • libvncserver Debian 14 0.9.15+dfsg-5

debian advisories DEBIAN-CVE-2026-44988

  • libvncserver Ubuntu 22.04 LTS 0.9.13+dfsg-3ubuntu0.1
  • libvncserver Ubuntu 24.04 LTS 0.9.14+dfsg-1ubuntu0.1
  • libvncserver Ubuntu 25.10 0.9.15+dfsg-1ubuntu0.1
  • libvncserver Ubuntu 26.04 LTS 0.9.15+dfsg-3ubuntu0.1

ubuntu advisories UBUNTU-CVE-2026-44988

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • LibVNCServer SLES for SAP applications 16.0, SLES 16.0 0.9.14-160000.5.1
  • LibVNCServer SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 0.9.14-150600.3.9.1
  • LibVNCServer SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 0.9.9-17.47.1

suse advisories SUSE-SU-2026:22190-1SUSE-SU-2026:2428-1SUSE-SU-2026:2427-1

  • LibVNCServer openSUSE Leap 16.0 0.9.14-160000.5.1
  • LibVNCServer openSUSE Tumbleweed 0.9.15-3.1

opensuse advisories openSUSE-SU-2026:21118-1openSUSE-SU-2026:10905-1

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
5 mo ago

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected products

  • LibVNC libvncserver

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.