CVE-2026-25128 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in fast-xml-parser. O3 Security confirms whether CVE-2026-25128 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
fast-xml-parser has RangeError DoS Numeric Entities Bug
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
fast-xml-parsernpmDescription
fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. In versions 5.0.9 through 5.3.3, a RangeError vulnerability exists in the numeric entity processing of fast-xml-parser when parsing XML with out-of-range entity code points (e.g., � or �). This causes the parser to throw an uncaught exception, crashing any application that processes untrusted XML input. Version 5.3.4 fixes the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fast-xml-parser | ≥ 5.0.9&&< 5.3.4 | 5.3.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fast-xml-parser. 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 fast-xml-parser to 5.3.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25128 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-2026-25128 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-2026-25128. 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-2026-25128 in your dependencies?
O3 detects CVE-2026-25128 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.