CVE-2025-66034: fontTools is a library for manipulating fonts, written in Python

Q: How do I fix CVE-2025-66034?

fonttools: upgrade to 4.60.2. Exact commands for each OS are on this page.

Q: Is CVE-2025-66034 being exploited?

CVE-2025-66034 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-66034 affect?

CVE-2025-66034 affects fonttools. Severity is medium (CVSS 6.3). 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 exe

Q: How urgent is CVE-2025-66034?

Priority 38/100. Public exploit reference

Routine

MEDIUM 6.3UPGRADE

CVE-2025-66034 is a medium-severity flaw (CVSS 6.3) affecting fonttools. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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(). Th

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	6.3 (Medium)
Attack vector	Local
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.5% (top 54%)
CISA exploited list	No
Weakness	CWE-91
Published	2025-11-29
Last modified	2026-10-18

Publisher (CNA): GitHub, Inc. · Vendor: fonttools

Last updated 2026-10-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-11-29 01:16 UTCPublished CVE record published
2026-10-18 18:10 UTCUpdated Record last modified

fonttools fonttools UPGRADE

Affected: >= 4.33.0 and < 4.60.2

Fixed in: 4.60.2

Safe to downgrade to: a release before 4.33.0

1. Check installed version

pip show fonttools

2. UPGRADE to 4.60.2

pip install --upgrade "fonttools>=4.60.2"

3. If no update is available yet, DOWNGRADE to a release before 4.33.0

pip index versions fonttools pip install "fonttools<4.33.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-66034?

fonttools: upgrade to 4.60.2. Exact commands for each OS are on this page.

Is CVE-2025-66034 being exploited?

CVE-2025-66034 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-66034 affect?

CVE-2025-66034 affects fonttools. Severity is medium (CVSS 6.3). 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 exe

How urgent is CVE-2025-66034?

Priority 38/100. Public exploit reference

Software pages

Python vulnerabilities

References

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