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

Source: https://junglewise.ai/threats/cve-2026-63276-libreoffice-converts-cff-fonts-to-type-1-when-it-subsets-a-font  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-22. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-63276 · Severity: info · Published 2026-09-22

LibreOffice can export documents to PDF and may embed CFF fonts in them. When converting these fonts to Type 1 format during subsetting, a buffer overflow vulnerability allows a malicious document to write data past a fixed-size buffer. An attacker with a crafted document could crash the application or potentially execute arbitrary code.

Technologies: [LibreOffice](https://junglewise.ai/threats/technologies/libreoffice-libreoffice). Vendors: [LibreOffice](https://junglewise.ai/threats/vendors/libreoffice).

## Quick answers

**Is CVE-2026-63276 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-63276 being exploited in the wild.

**How severe is CVE-2026-63276?** Informational severity, published 22 September 2026.

**Which products and versions are affected?** LibreOffice before 26.2.5.

**Is there a fix for CVE-2026-63276?** A patch was published on 2026-09-21: Fixed in LibreOffice 26.2.5 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-63276 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-63276?** Check whether you run LibreOffice at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A stack buffer overflow exists in LibreOffice's CFF to Type 1 font conversion routine, which occurs during PDF export when fonts are subsetted. Converted font operators are written into a fixed-size buffer without bounds checking; a glyph emitting many operators will overflow the stack buffer. The attack vector is opening a malicious document with embedded CFF fonts and exporting to PDF.

## Affected products

- LibreOffice LibreOffice before 26.2.5

## Timeline

- 2026-09-21: disclosed
- 2026-09-21: patched: Fixed in LibreOffice 26.2.5

## References

- [https://www.libreoffice.org/about-us/security/advisories/cve-2026-63276](https://www.libreoffice.org/about-us/security/advisories/cve-2026-63276)

## Related threats

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- [LibreOffice out of bounds read in PICT image import](https://junglewise.ai/threats/cve-2026-63279-libreoffice-can-import-pict-images-which-may-be-embedded-in)
- [LibreOffice stack buffer overflow in CFF font hint handling](https://junglewise.ai/threats/cve-2026-63275-libreoffice-can-read-cff-fonts-which-may-be-embedded-in-documents)
- [LibreOffice heap buffer overflow in WMF text record import](https://junglewise.ai/threats/cve-2026-63272-libreoffice-can-import-wmf-graphics-which-may-be-embedded-in)