Description
LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, a malicious (or man-in-the-middle) VNC server can force a connecting `libvncclient` to write attacker-controlled data past the end of its framebuffer. This is an out-of-bounds heap write with attacker-controlled length, contents, and offset. It needs no authentication (the attacker is the server), works in a default build with default settings, and fires from a single `FramebufferUpdate` the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue.
References3
Metrics
- CVSS 3.1
-
8.8
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - EPSS — exploit probability
- 0% percentile: 35 · as of 9 November 2026
- CWE
- CWE-122CWE-787
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.