# CVE-2026-6040: Heap use-after-free in ODF number-format blank-width parsing

> A heap use-after-free in LibreOffice allows attackers to execute arbitrary code or cause denial of service via a malformed ODF number format.

- **Severity:** Medium 5.4 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N/E:P`)
- **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:** 15 Jun 2026
- **Updated:** 23 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-6040, GHSA-pp4w-c8m6-4xvf, UBUNTU-CVE-2026-6040

## What is CVE-2026-6040?

CVE-2026-6040 is a medium-severity use after free vulnerability in The Document Foundation LibreOffice, published on 15 Jun 2026. 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

A heap use-after-free existed when importing the blank-width characters of an ODF number format. A position value read from the document was not checked against the length of the format-code string, so a malformed number format could be processed against memory outside that string. In fixed versions the position is bounds-checked before use.

Weakness: CWE-825 (Expired Pointer Dereference), CWE-787 (Out-of-bounds Write), CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-6040?


## How do I fix CVE-2026-6040?

Apply the vendor's patch.

## Is CVE-2026-6040 being exploited?

There is no known exploitation of CVE-2026-6040 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6040 and fix it if it is affected.

What it is: CVE-2026-6040 is a medium-severity use after free vulnerability in The Document Foundation LibreOffice, published on 15 Jun 2026. 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-2026-6040 in the wild and no public exploit code.

Affected product: The Document Foundation LibreOffice. 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-2026-6040/ (Markdown: https://insights.sbomify.com/CVE-2026-6040/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6040
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6040
- OSV: https://osv.dev/vulnerability/CVE-2026-6040

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6040/
Summaries are generated and may contain mistakes; the official description above is the record.