# CVE-2021-24031: Information disclosure in Zstandard

> Local attackers can read or modify Zstandard output files due to insecure default permissions before completion.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-24031, CLEANSTART-2025-NH78236, DEBIAN-CVE-2021-24031, DLA-2573-1, DSA-4850-1, GHSA-5mqj-v3fr-pg3x, MGASA-2021-0322, UBUNTU-CVE-2021-24031

## What is CVE-2021-24031?

CVE-2021-24031 is a medium-severity vulnerability in Facebook Zstandard, published on 4 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Zstandard command-line utility prior to v1.4.1, output files were created with default permissions. Correct file permissions (matching the input) would only be set at completion time. Output files could therefore be readable or writable to unintended parties.

Weakness: CWE-276 (Incorrect Default Permissions), CWE-277 (Insecure Inherited Permissions)

## Which versions are affected by CVE-2021-24031?

It affects 1 product.


Products: Facebook Zstandard.

## How do I fix CVE-2021-24031?

Upgrade to a fixed version.

## Is CVE-2021-24031 being exploited?

There is no known exploitation of CVE-2021-24031 in the wild and no public exploit code.

## Other vulnerabilities in Facebook Zstandard

- [CVE-2019-11922](https://insights.sbomify.com/CVE-2019-11922/): Race condition in Zstandard (high 8.1)
- [CVE-2022-4899](https://insights.sbomify.com/CVE-2022-4899/): zstd vulnerable to buffer overrun (high 7.5)
- [CVE-2021-24032](https://insights.sbomify.com/CVE-2021-24032/): Information disclosure in Zstandard (medium 4.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-24031 and fix it if it is affected.

What it is: CVE-2021-24031 is a medium-severity vulnerability in Facebook Zstandard, published on 4 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-24031 in the wild and no public exploit code.

Affected product: Facebook Zstandard. 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-2021-24031/ (Markdown: https://insights.sbomify.com/CVE-2021-24031/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-24031
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-24031
- OSV: https://osv.dev/vulnerability/CVE-2021-24031

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-24031/
Summaries are generated and may contain mistakes; the official description above is the record.