CVE-2023-34104 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in fast-xml-parser. O3 Security confirms whether CVE-2023-34104 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Regex Injection via Doctype Entities
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 is an open source, pure javascript xml parser. fast-xml-parser allows special characters in entity names, which are not escaped or sanitized. Since the entity name is used for creating a regex for searching and replacing entities in the XML body, an attacker can abuse it for denial of service (DoS) attacks. By crafting an entity name that results in an intentionally bad performing regex and utilizing it in the entity replacement step of the parser, this can cause the parser to stall for an indefinite amount of time. This problem has been resolved in v4.2.4. Users are advised to upgrade. Users unable to upgrade should avoid using DOCTYPE parsing by setting the processEntities: false option.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fast-xml-parser | ≥ 4.1.3&&< 4.2.4 | 4.2.4 |
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 4.2.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-34104 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-2023-34104 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-2023-34104. 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-2023-34104 in your dependencies?
O3 detects CVE-2023-34104 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.