# CVE-2023-6683: Qemu: vnc: null pointer dereference in qemu_clipboard_request()

> A malicious authenticated VNC client can crash QEMU via a null pointer dereference in the clipboard request handler, causing denial of service.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Jan 2024
- **Updated:** 25 Feb 2026
- **Also known as:** AZL-40048, AZL-43054, BELL-CVE-2023-6683, DEBIAN-CVE-2023-6683, GHSA-x9c6-9g9w-hg73, UBUNTU-CVE-2023-6683

## What is CVE-2023-6683?

CVE-2023-6683 is a medium-severity vulnerability in Qemu Qemu, published on 12 Jan 2024. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A flaw was found in the QEMU built-in VNC server while processing ClientCutText messages. The qemu_clipboard_request() function can be reached before vnc_server_cut_text_caps() was called and had the chance to initialize the clipboard peer, leading to a NULL pointer dereference. This could allow a malicious authenticated VNC client to crash QEMU and trigger a denial of service.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2023-6683?

It affects 2 products.


Products: Qemu Qemu, Redhat Enterprise Linux.

## How do I fix CVE-2023-6683?

Apply the vendor's patch.

## Is CVE-2023-6683 being exploited?

There is no known exploitation of CVE-2023-6683 in the wild and no public exploit code.

## Other vulnerabilities in Qemu Qemu

- [CVE-2022-36648](https://insights.sbomify.com/CVE-2022-36648/): Null dereference in n/a (critical 10.0)
- [CVE-2015-8556](https://insights.sbomify.com/CVE-2015-8556/): Race condition in n/a (critical 10.0)
- [CVE-2009-3616](https://insights.sbomify.com/CVE-2009-3616/): Use after free in n/a (critical 9.9)
- [CVE-2019-12928](https://insights.sbomify.com/CVE-2019-12928/): Command injection in n/a (critical 9.8)
- [CVE-2019-12929](https://insights.sbomify.com/CVE-2019-12929/): Command injection in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-6683 and fix it if it is affected.

What it is: CVE-2023-6683 is a medium-severity vulnerability in Qemu Qemu, published on 12 Jan 2024. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-6683 in the wild and no public exploit code.

Affected product: Qemu Qemu. 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-2023-6683/ (Markdown: https://insights.sbomify.com/CVE-2023-6683/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-6683
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-6683
- OSV: https://osv.dev/vulnerability/CVE-2023-6683

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-6683/
Summaries are generated and may contain mistakes; the official description above is the record.