# CVE-2021-3516: Use after free in libxml2

> An attacker can trigger a use-after-free in libxml2's xmllint via a crafted file, potentially leading to code execution or denial of service.

- **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:** 1 Jun 2021
- **Updated:** 14 Oct 2026
- **Also known as:** DEBIAN-CVE-2021-3516, GHSA-cfj9-6cq4-25vj, UBUNTU-CVE-2021-3516

## What is CVE-2021-3516?

CVE-2021-3516 is a high-severity use after free vulnerability in Debian Debian Linux, published on 1 Jun 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

There's a flaw in libxml2's xmllint in versions before 2.9.11. An attacker who is able to submit a crafted file to be processed by xmllint could trigger a use-after-free. The greatest impact of this flaw is to confidentiality, integrity, and availability.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-3516?

It affects 9 products.


Products: Debian Debian Linux, Fedoraproject Fedora, Netapp Clustered Data Ontap, Netapp Clustered Data Ontap Antivirus Connector, Netapp Ontap Select Deploy Administration Utility, Oracle Zfs Storage Appliance Kit, Redhat Enterprise Linux, Redhat Jboss Core Services, Xmlsoft Xmllint.

## How do I fix CVE-2021-3516?

Upgrade to a fixed version.

## Is CVE-2021-3516 being exploited?

There is no known exploitation of CVE-2021-3516 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3516 and fix it if it is affected.

What it is: CVE-2021-3516 is a high-severity use after free vulnerability in Debian Debian Linux, published on 1 Jun 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-2021-3516 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2021-3516/ (Markdown: https://insights.sbomify.com/CVE-2021-3516/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3516
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3516
- OSV: https://osv.dev/vulnerability/CVE-2021-3516

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3516/
Summaries are generated and may contain mistakes; the official description above is the record.