# CVE-2018-6307: Use after free in LibVNC

> A heap use-after-free in LibVNC's file transfer extension allows remote attackers to execute arbitrary code.

- **Severity:** High 8.1 (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/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:** Not needed
- **Fix available:** Yes
- **Published:** 19 Dec 2018
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2018-6307, GHSA-862p-2jpg-8gg4, UBUNTU-CVE-2018-6307

## What is CVE-2018-6307?

CVE-2018-6307 is a high-severity use after free vulnerability in Canonical Ubuntu Linux, published on 19 Dec 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

LibVNC before commit ca2a5ac02fbbadd0a21fabba779c1ea69173d10b contains heap use-after-free vulnerability in server code of file transfer extension that can result remote code execution.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2018-6307?

It affects 3 products.


Products: Canonical Ubuntu Linux, Debian Debian Linux, Libvnc Project Libvncserver.

## How do I fix CVE-2018-6307?

Apply the vendor's patch.

## Is CVE-2018-6307 being exploited?

There is no known exploitation of CVE-2018-6307 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-6307 and fix it if it is affected.

What it is: CVE-2018-6307 is a high-severity use after free vulnerability in Canonical Ubuntu Linux, published on 19 Dec 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-6307 in the wild and no public exploit code.

Affected product: Canonical Ubuntu Linux. 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-2018-6307/ (Markdown: https://insights.sbomify.com/CVE-2018-6307/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-6307
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-6307
- OSV: https://osv.dev/vulnerability/CVE-2018-6307

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-6307/
Summaries are generated and may contain mistakes; the official description above is the record.