# CVE-2026-50538: libvncclient Tight decoder has an attacker-controlled heap out-of-bounds write

> A malicious VNC server can trigger a heap out-of-bounds write in libvncclient, leading to remote code execution or denial of service upon connection.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 21 Aug 2026
- **Updated:** 24 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-50538, GHSA-v9pm-47h4-jcq8, OESA-2026-3318, OESA-2026-3319, OESA-2026-3320, OESA-2026-3489, SUSE-SU-2026:23601-1, SUSE-SU-2026:3803-1, SUSE-SU-2026:4022-1, SUSE-SU-2026:4024-1, UBUNTU-CVE-2026-50538, USN-8494-1, openSUSE-SU-2026:11601-1, openSUSE-SU-2026:21735-1

## What is CVE-2026-50538?

CVE-2026-50538 is a high-severity memory corruption vulnerability in libvncserver, published on 21 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-787 (Out-of-bounds Write), CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-50538?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `LibVNCServer` | SUSE:Linux Enterprise Module for Package Hub 15 SP7 | All versions | 0.9.10-150000.4.41.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Module for Package Hub 15 SP7 | All versions | 0.9.14-150600.3.12.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server 12 SP5-LTSS | All versions | 0.9.9-17.50.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server 16.0 | All versions | 0.9.14-160000.6.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | All versions | 0.9.9-17.50.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 0.9.14-160000.6.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Workstation Extension 15 SP7 | All versions | 0.9.14-150600.3.12.1 |
| `LibVNCServer` | openSUSE:Leap 16.0 | All versions | 0.9.14-160000.6.1 |
| `LibVNCServer` | openSUSE:Tumbleweed | All versions | 0.9.15-4.1 |

## How do I fix CVE-2026-50538?

Apply the vendor's patch.

## Is CVE-2026-50538 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-50538 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-50538 and fix it if it is affected.

What it is: CVE-2026-50538 is a high-severity memory corruption vulnerability in libvncserver, published on 21 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-50538 exists.

Affected product: libvncserver. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-50538/ (Markdown: https://insights.sbomify.com/CVE-2026-50538/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-50538
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-50538
- OSV: https://osv.dev/vulnerability/CVE-2026-50538

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-50538/
Summaries are generated and may contain mistakes; the official description above is the record.