# CVE-2026-63660: node-fontnik: integer-overflow heap out-of-bounds write in RenderSDF

Status: published. Published: 2026-11-11. Updated: 2026-11-11.

node-fontnik is a library that delivers a range of glyphs rendered as SDFs (signed distance fields) in a protocol buffer. Prior to version 0.7.7, a crafted font could trigger a heap out-of-bounds write in RenderSDF (include/mapbox/glyph_foundry_impl.hpp). RenderSDF computed the SDF bitmap allocation size as buffered_width * buffered_height in 32-bit unsigned int. Glyph dimensions are derived from the uploaded font's outline bounding box with no upper bound, so a glyph large enough to make that product exceed 2³² wrapped to a small value. The buffer was then under-allocated while the render loop still wrote one byte per pixel, corrupting the heap (CWE-190 → CWE-787) and crashing the process. A 680-byte font is enough to drive FreeType to a 65536×65536 buffered glyph, wrapping the size to 0. This issue has been patched in version 0.7.7.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- mapbox / node-fontnik: < 0.7.7 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 8.1 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-190, CWE-787

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/mapbox/node-fontnik/pull/202 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/mapbox/node-fontnik/releases/tag/v0.7.7 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-63660; retrieved 2026-11-11; source updated 2026-11-11

Revision: aed41291cd02cd9da39e87c2ce699701c592511feb2bf544c4c23ab5e72261db

Canonical: https://y2.dev/cve/CVE-2026-63660

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