# CVE-2021-4127: Other in Firefox ESR

> Outdated graphics library in Thunderbird and Firefox ESR may allow attackers to execute arbitrary code via potential vulnerabilities.

- **Severity:** Critical 9.8 (`CVSS:3.1/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:** 22 Dec 2022
- **Updated:** 16 Apr 2025
- **Also known as:** DEBIAN-CVE-2021-4127, GHSA-7wp9-fj5q-c4jc

## What is CVE-2021-4127?

CVE-2021-4127 is a critical vulnerability in Mozilla Firefox Esr, published on 22 Dec 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An out of date graphics library (Angle) likely contained vulnerabilities that could potentially be exploited. This vulnerability affects Thunderbird < 78.9 and Firefox ESR < 78.9.

## Which versions are affected by CVE-2021-4127?

It affects 2 products.


Products: Mozilla Firefox Esr, Mozilla Thunderbird.

## How do I fix CVE-2021-4127?

Upgrade to a fixed version.

## Is CVE-2021-4127 being exploited?

There is no known exploitation of CVE-2021-4127 in the wild and no public exploit code.

## Other vulnerabilities in Mozilla Firefox Esr

- [CVE-2023-25746](https://insights.sbomify.com/CVE-2023-25746/): Memory corruption in Firefox ESR (high 8.8)
- [CVE-2021-38495](https://insights.sbomify.com/CVE-2021-38495/): Memory corruption in Firefox ESR (high 8.8)
- [CVE-2020-15669](https://insights.sbomify.com/CVE-2020-15669/): Use after free in Firefox ESR (high 8.8)
- [CVE-2022-38476](https://insights.sbomify.com/CVE-2022-38476/): Use after free in Firefox ESR (high 7.5)
- [CVE-2020-6828](https://insights.sbomify.com/CVE-2020-6828/): Path traversal in Firefox ESR (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-4127 and fix it if it is affected.

What it is: CVE-2021-4127 is a critical vulnerability in Mozilla Firefox Esr, published on 22 Dec 2022. 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-2021-4127 in the wild and no public exploit code.

Affected product: Mozilla Firefox Esr. 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-2021-4127/ (Markdown: https://insights.sbomify.com/CVE-2021-4127/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-4127
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-4127
- OSV: https://osv.dev/vulnerability/CVE-2021-4127

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-4127/
Summaries are generated and may contain mistakes; the official description above is the record.