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.
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.
Analysis
No analysis available yet.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| LibVNC | libvncserver | affected |
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No data available yet.
Remediation
No remediation available yet.
Tracking
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Advisories
| Source | ID | Title |
|---|---|---|
 Ubuntu USN |
USN-8494-1 | LibVNCServer vulnerability |
References
History
Fri, 21 Aug 2026 21:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | libvncclient Tight decoder has an attacker-controlled heap out-of-bounds write | |
| Weaknesses | CWE-122 CWE-787 |
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| References |
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| Metrics |
cvssV3_1
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Subscriptions
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MITRE
Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-08-21T21:03:58.147Z
Reserved: 2026-06-04T20:37:18.653Z
Link: CVE-2026-50538
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-21T21:16:59.807
Modified: 2026-08-21T21:16:59.807
Link: CVE-2026-50538
Redhat
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OpenCVE Enrichment
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