CVE-2023-45139
HIGHfonttools XML External Entity Injection (XXE) Vulnerability
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
fonttoolsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | fonttools | ≥ 4.28.2&&< 4.43.0 | 4.43.0 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fonttools. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update fonttools to 4.43.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-45139 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2023-45139 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2023-45139. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-45139 in your dependencies?
O3 detects CVE-2023-45139 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.