medium CVSS 6.3

CVE-2025-66034·Python vulnerability

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.

Severity
medium
Software
Python
Fixed in
4.60.2
Published
2025-11-29

Affected versions

From: 4.33.0

Until: 4.60.2

Fixed in: 4.60.2

How to fix this CVE

Update fontTools to version 4.60.2 or later to patch a file write vulnerability in the varLib module that could allow code execution through malicious .designspace files. Users relying on fontTools for font processing should prioritize this update, especially if processing untrusted font design files from external sources.

sudo dnf update python3-fonttools

Defensia detects this vulnerability

How to check if you are affected

  1. Run `pip show fonttools` or `python3 -c "import fontTools; print(fontTools.__version__)"` to check the installed fontTools version
  2. Verify if fontTools.varLib is imported or used in your Python applications by searching codebase: `grep -r "from fontTools.varLib import\|fontTools.varLib.main" /path/to/app`
  3. Check process execution logs for invocations of `python3 -m fontTools.varLib` or similar: `grep -i "fonttools.*varlib\|designspace" /var/log/auth.log /var/log/syslog`
  4. Confirm the patch by running `pip show fonttools | grep Version` and verifying the version is 4.60.2 or higher

FAQ

What is CVE-2025-66034?

CVE-2025-66034 is a file write vulnerability in fontTools' varLib module that allows attackers to execute arbitrary code by crafting malicious .designspace font configuration files. When processed, the vulnerable code fails to safely handle file paths, enabling an attacker to write files to arbitrary locations.

Is CVE-2025-66034 being actively exploited?

No, CVE-2025-66034 is not currently listed in the CISA Known Exploited Vulnerabilities catalog, and no public exploits are available. However, the vulnerability should still be patched promptly to prevent future exploitation.

What versions of fontTools are affected by CVE-2025-66034?

Versions 4.33.0 through 4.60.1 are vulnerable. The vulnerability was patched in version 4.60.2 and later.

How do I check if my server is vulnerable to CVE-2025-66034?

Run `python3 -c "import fontTools; print(fontTools.__version__)"` and compare the version against 4.60.2. If your version is below 4.60.2, your installation is vulnerable.

Does Defensia detect CVE-2025-66034?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If fontTools is installed on a monitored server, CVE-2025-66034 will appear in your dashboard with remediation steps.

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References

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