# CVE-2021-38495: Memory corruption in Firefox ESR

> Memory safety bugs in Thunderbird allow attackers to potentially execute arbitrary code via crafted content.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 3 Nov 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-whqc-prwr-5mvr, UBUNTU-CVE-2021-38495

## What is CVE-2021-38495?

CVE-2021-38495 is a high-severity memory corruption vulnerability in Mozilla Firefox Esr, published on 3 Nov 2021. 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

Mozilla developers reported memory safety bugs present in Thunderbird 78.13.0. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Thunderbird < 91.1 and Firefox ESR < 91.1.

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

## Which versions are affected by CVE-2021-38495?

It affects 2 products.


Products: Mozilla Firefox Esr, Mozilla Thunderbird.

## How do I fix CVE-2021-38495?

Upgrade to a fixed version.

## Is CVE-2021-38495 being exploited?

There is no known exploitation of CVE-2021-38495 in the wild and no public exploit code.

## Other vulnerabilities in Mozilla Firefox Esr

- [CVE-2021-4127](https://insights.sbomify.com/CVE-2021-4127/): Other in Firefox ESR (critical 9.8)
- [CVE-2023-25746](https://insights.sbomify.com/CVE-2023-25746/): 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-2021-38495 and fix it if it is affected.

What it is: CVE-2021-38495 is a high-severity memory corruption vulnerability in Mozilla Firefox Esr, published on 3 Nov 2021. 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-2021-38495 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-2021-38495/ (Markdown: https://insights.sbomify.com/CVE-2021-38495/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-38495
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-38495
- OSV: https://osv.dev/vulnerability/CVE-2021-38495

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-38495/
Summaries are generated and may contain mistakes; the official description above is the record.