# CVE-2021-33574: Use after free in n/a

> A use-after-free in glibc's mq_notify function allows attackers to cause application crashes or potentially other impacts via crafted thread attributes.

- **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:** 25 May 2021
- **Updated:** 14 Oct 2026
- **Also known as:** DEBIAN-CVE-2021-33574, GHSA-rx5m-j84j-22pg, MGASA-2021-0308, OESA-2021-1239, SUSE-SU-2021:3290-1, UBUNTU-CVE-2021-33574

## What is CVE-2021-33574?

CVE-2021-33574 is a critical use after free vulnerability in Debian Debian Linux, published on 25 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The mq_notify function in the GNU C Library (aka glibc) versions 2.32 and 2.33 has a use-after-free. It may use the notification thread attributes object (passed through its struct sigevent parameter) after it has been freed by the caller, leading to a denial of service (application crash) or possibly unspecified other impact.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-33574?

It affects 13 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `glibc` | SUSE:Linux Enterprise Server 12 SP4-LTSS | All versions | 2.22-114.15.1 |
| `glibc` | SUSE:Linux Enterprise Server 12 SP5 | All versions | 2.22-114.15.1 |
| `glibc` | SUSE:Linux Enterprise Server for SAP Applications 12 SP4 | All versions | 2.22-114.15.1 |
| `glibc` | SUSE:Linux Enterprise Server for SAP Applications 12 SP5 | All versions | 2.22-114.15.1 |
| `glibc` | SUSE:Linux Enterprise Software Development Kit 12 SP5 | All versions | 2.22-114.15.1 |
| `glibc` | SUSE:OpenStack Cloud 9 | All versions | 2.22-114.15.1 |
| `glibc` | SUSE:OpenStack Cloud Crowbar 9 | All versions | 2.22-114.15.1 |

Products: Debian Debian Linux, Fedoraproject Fedora, Gnu Glibc, Netapp Cloud Backup, Netapp E-Series Santricity Os Controller, Netapp H300e Firmware, Netapp H300s Firmware, Netapp H410s Firmware, Netapp H500e Firmware, Netapp H500s Firmware, Netapp H700e Firmware, Netapp H700s Firmware, Netapp Solidfire Baseboard Management Controller Firmware.

## How do I fix CVE-2021-33574?

Apply the vendor's patch.

## Is CVE-2021-33574 being exploited?

There is no known exploitation of CVE-2021-33574 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-2021-33574 and fix it if it is affected.

What it is: CVE-2021-33574 is a critical use after free vulnerability in Debian Debian Linux, published on 25 May 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-2021-33574 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-2021-33574/ (Markdown: https://insights.sbomify.com/CVE-2021-33574/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33574
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33574
- OSV: https://osv.dev/vulnerability/CVE-2021-33574

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-33574/
Summaries are generated and may contain mistakes; the official description above is the record.