# CVE-2020-11721: Use after free in n/a

> An attacker can cause a denial of service in applications using libsixel by triggering an invalid free operation via a crafted PNG file.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:** 12 Apr 2020
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-11721, GHSA-99gh-8v88-fprw, UBUNTU-CVE-2020-11721

## What is CVE-2020-11721?

CVE-2020-11721 is a medium-severity use after free vulnerability in n/a, published on 12 Apr 2020. 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

load_png in loader.c in libsixel.a in libsixel 1.8.6 has an uninitialized pointer leading to an invalid call to free, which can cause a denial of service.

Weakness: CWE-824 (Access of Uninitialized Pointer)

## Which versions are affected by CVE-2020-11721?

It affects 1 product.


Products: Saitoha Libsixel.

## How do I fix CVE-2020-11721?

Upgrade to a fixed version.

## Is CVE-2020-11721 being exploited?

There is no known exploitation of CVE-2020-11721 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2019-19635](https://insights.sbomify.com/CVE-2019-19635/): Memory corruption in n/a (critical 9.8)
- [CVE-2019-19636](https://insights.sbomify.com/CVE-2019-19636/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-19637](https://insights.sbomify.com/CVE-2019-19637/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-19638](https://insights.sbomify.com/CVE-2019-19638/): Integer overflow in n/a (critical 9.8)
- [CVE-2022-27044](https://insights.sbomify.com/CVE-2022-27044/): Memory corruption in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-11721 and fix it if it is affected.

What it is: CVE-2020-11721 is a medium-severity use after free vulnerability in n/a, published on 12 Apr 2020. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2020-11721 in the wild and no public exploit code.

Affected product: n/a. 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-2020-11721/ (Markdown: https://insights.sbomify.com/CVE-2020-11721/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-11721
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-11721
- OSV: https://osv.dev/vulnerability/CVE-2020-11721

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-11721/
Summaries are generated and may contain mistakes; the official description above is the record.