XPath Injection in Fonttools

CVE-2025-66034

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.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 6.3 (Medium). Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:L.

EPSS exploit prediction

EPSS: 0.005 (43.7th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 44th percentile — 43.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2025-66034: held from 0.005 to 0.005.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2025-66034?
CVE-2025-66034 is a medium-severity vulnerability in Fonttools, classified under XML Injection (Blind XPath Injection). CVSS score: 6.3/10. Published 2025-11-29.
How severe is CVE-2025-66034?
Medium severity. CVSS v3 base score is 6.3 out of 10.
Is CVE-2025-66034 known to be exploited?
6 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.