# CVE-2018-20020: Memory corruption in LibVNC

> A heap out-of-bound write in LibVNC allows remote attackers to execute arbitrary code via malicious VNC server responses.

- **Severity:** Critical 9.8 (`CVSS:3.0/AV:N/AC:L/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-2018-20020, GHSA-v93r-hw5v-g7wc, UBUNTU-CVE-2018-20020

## What is CVE-2018-20020?

CVE-2018-20020 is a critical memory corruption 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 7b1ef0ffc4815cab9a96c7278394152bdc89dc4d contains heap out-of-bound write vulnerability inside structure in VNC client code that can result remote code execution

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2018-20020?

It affects 3 products.


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

## How do I fix CVE-2018-20020?

Apply the vendor's patch.

## Is CVE-2018-20020 being exploited?

There is no known exploitation of CVE-2018-20020 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-2018-20020 and fix it if it is affected.

What it is: CVE-2018-20020 is a critical memory corruption 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-2018-20020 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-2018-20020/ (Markdown: https://insights.sbomify.com/CVE-2018-20020/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-20020
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-20020
- OSV: https://osv.dev/vulnerability/CVE-2018-20020

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-20020/
Summaries are generated and may contain mistakes; the official description above is the record.