# CVE-2021-3403: Use after free in ytnef

> A double free vulnerability in the ytnef library allows remote attackers to cause denial of service and potentially execute code via a crafted file.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/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:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 4 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3403, GHSA-4pxg-g29h-qqfc, UBUNTU-CVE-2021-3403

## What is CVE-2021-3403?

CVE-2021-3403 is a high-severity use after free vulnerability in Fedoraproject Fedora, published on 4 Mar 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

In ytnef 1.9.3, the TNEFSubjectHandler function in lib/ytnef.c allows remote attackers to cause a denial-of-service (and potentially code execution) due to a double free which can be triggered via a crafted file.

Weakness: CWE-415 (Double Free), CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-3403?

It affects 3 products.


Products: Fedoraproject Fedora, Redhat Enterprise Linux, Ytnef Project Ytnef.

## How do I fix CVE-2021-3403?

Apply the vendor's patch.

## Is CVE-2021-3403 being exploited?

There is no known exploitation of CVE-2021-3403 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3403 and fix it if it is affected.

What it is: CVE-2021-3403 is a high-severity use after free vulnerability in Fedoraproject Fedora, published on 4 Mar 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-3403 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2021-3403/ (Markdown: https://insights.sbomify.com/CVE-2021-3403/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3403
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3403
- OSV: https://osv.dev/vulnerability/CVE-2021-3403

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3403/
Summaries are generated and may contain mistakes; the official description above is the record.