# CVE-2021-40439: Billion Laughs

> An attacker can cause a denial of service in Apache OpenOffice by exploiting an XML entity expansion vulnerability in the bundled expat library via crafted ODF files.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 7 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-7579-q6rq-wf6r

## What is CVE-2021-40439?

CVE-2021-40439 is a medium-severity vulnerability in Apache Openoffice, published on 7 Oct 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Apache OpenOffice has a dependency on expat software. Versions prior to 2.1.0 were subject to CVE-2013-0340 a "Billion Laughs" entity expansion denial of service attack and exploit via crafted XML files. ODF files consist of a set of XML files. All versions of Apache OpenOffice up to 4.1.10 are subject to this issue. expat in version 4.1.11 is patched.

Weakness: CWE-611 (Improper Restriction of XML External Entity Reference)

## Which versions are affected by CVE-2021-40439?

It affects 1 product.


Products: Apache Openoffice.

## How do I fix CVE-2021-40439?

No fix has been published for CVE-2021-40439 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-40439 being exploited?

There is no known exploitation of CVE-2021-40439 in the wild and no public exploit code.

## Other vulnerabilities in Apache Openoffice

- [CVE-2014-3524](https://insights.sbomify.com/CVE-2014-3524/): Command injection in n/a (critical 9.3)
- [CVE-2010-3450](https://insights.sbomify.com/CVE-2010-3450/): Path traversal in n/a (critical 9.3)
- [CVE-2010-3451](https://insights.sbomify.com/CVE-2010-3451/): Use after free in n/a (critical 9.3)
- [CVE-2010-3452](https://insights.sbomify.com/CVE-2010-3452/): Use after free in n/a (critical 9.3)
- [CVE-2010-3453](https://insights.sbomify.com/CVE-2010-3453/): Memory corruption in n/a (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40439 and fix it if it is affected.

What it is: CVE-2021-40439 is a medium-severity vulnerability in Apache Openoffice, published on 7 Oct 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-40439 in the wild and no public exploit code.

Affected product: Apache Openoffice. 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-2021-40439/ (Markdown: https://insights.sbomify.com/CVE-2021-40439/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40439
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40439
- OSV: https://osv.dev/vulnerability/CVE-2021-40439

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-40439/
Summaries are generated and may contain mistakes; the official description above is the record.