# CVE-2026-63276: Stack buffer overflow in CFF to Type 1 font conversion

> A stack buffer overflow in LibreOffice's CFF to Type 1 font conversion allows attackers to execute arbitrary code or cause a crash via malicious documents.

- **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:** 22 Sep 2026
- **Updated:** 22 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-63276, ECHO-5352-3f6e-0c72, GHSA-3xpv-4h8q-pj26, MINI-mhqq-m3gr-8vvh, UBUNTU-CVE-2026-63276

## What is CVE-2026-63276?

CVE-2026-63276 is a medium-severity memory corruption vulnerability in The Document Foundation LibreOffice, published on 22 Sep 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

LibreOffice converts CFF fonts to Type 1 when it subsets a font, which happens when a document is exported to PDF, and CFF fonts may be embedded in documents. A stack buffer overflow existed in that conversion. The converted operators were written into a fixed size buffer with no check that they still fit, so a glyph emitting many operators wrote past the end of the buffer. In fixed versions the remaining capacity is tracked and the conversion stops when it is used up.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-63276?


## How do I fix CVE-2026-63276?

Apply the vendor's patch.

## Is CVE-2026-63276 being exploited?

There is no known exploitation of CVE-2026-63276 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63276 and fix it if it is affected.

What it is: CVE-2026-63276 is a medium-severity memory corruption vulnerability in The Document Foundation LibreOffice, published on 22 Sep 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-2026-63276 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-2026-63276/ (Markdown: https://insights.sbomify.com/CVE-2026-63276/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63276
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63276
- OSV: https://osv.dev/vulnerability/CVE-2026-63276

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-63276/
Summaries are generated and may contain mistakes; the official description above is the record.