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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 0.7.7
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. A crafted font is rendered, producing a glyph large enough that buffered width times height exceeds 2^32.
- Published
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 16/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
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.
Read the original 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.
Who should check
Teams running node-fontnik before 0.7.7 that render fonts supplied by users or other untrusted sources.
Read the source excerpt
“A crafted font could trigger a heap out-of-bounds write in RenderSDF”
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure8/25Specific setups only, reachable over the network
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.1/10CVSS 8.1
- No patch0/5No signal
What would change the score
- Would score about 66 if added to CISA KEV
- Would score about 61 if CISA's SSVC rates exploitation active
- Would score about 23 if CISA's SSVC rates it automatable
What to do
Check whether your setup matches what the bug needs.
A crafted font is rendered, producing a glyph large enough that buffered width times height exceeds 2^32.Upgrade to a fixed version: 0.7.7.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
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.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- mapbox node-fontnik
fixed in 0.7.7
Evidence 5
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 2
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-63660
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: cve.now feed data
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: github.com
Which versions are affected by CVE-2026-63660?
node-fontnik: before 0.7.7.Source: cve.now feed data
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: github.com
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: github.com