# CVE-2021-20231: Use after free in gnutls

> A use-after-free flaw in GnuTLS allows attackers to cause memory corruption, potentially leading to code execution or denial of service.

- **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:** 12 Mar 2021
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2021-20231, AZL-6446, DEBIAN-CVE-2021-20231, GHSA-mqq9-xchh-h97q, JLSEC-2026-520, UBUNTU-CVE-2021-20231

## What is CVE-2021-20231?

CVE-2021-20231 is a critical use after free vulnerability in Fedoraproject Fedora, published on 12 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in gnutls. A use after free issue in client sending key_share extension may lead to memory corruption and other consequences.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-20231?

It affects 5 products.


Products: Fedoraproject Fedora, Gnu Gnutls, Netapp Active Iq Unified Manager, Netapp E-Series Performance Analyzer, Redhat Enterprise Linux.

## How do I fix CVE-2021-20231?

Upgrade to a fixed version.

## Is CVE-2021-20231 being exploited?

There is no known exploitation of CVE-2021-20231 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-2021-20231 and fix it if it is affected.

What it is: CVE-2021-20231 is a critical use after free vulnerability in Fedoraproject Fedora, published on 12 Mar 2021. 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-2021-20231 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-2021-20231/ (Markdown: https://insights.sbomify.com/CVE-2021-20231/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20231
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20231
- OSV: https://osv.dev/vulnerability/CVE-2021-20231

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20231/
Summaries are generated and may contain mistakes; the official description above is the record.