Vulnerability Description
fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Versions 4.0.0-beta.3 through 5.5.5 contain a bypass vulnerability where numeric character references (&#NNN;, &#xHH;) and standard XML entities completely evade the entity expansion limits (e.g., maxTotalExpansions, maxExpandedLength) added to fix CVE-2026-26278, enabling XML entity expansion Denial of Service. The root cause is that replaceEntitiesValue() in OrderedObjParser.js only enforces expansion counting on DOCTYPE-defined entities while the lastEntities loop handling numeric/standard entities performs no counting at all. An attacker supplying 1M numeric entity references like A can force ~147MB of memory allocation and heavy CPU usage, potentially crashing the process—even when developers have configured strict limits. This issue has been fixed in version 5.5.6.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Naturalintelligence | Fast-Xml-Parser | >= 4.0.1, < 5.5.6 |
Related Weaknesses (CWE)
References
- https://github.com/NaturalIntelligence/fast-xml-parser/commit/bd26122c838e6a55e7Patch
- https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.5.6ProductRelease Notes
- https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-ExploitMitigationVendor Advisory
FAQ
What is CVE-2026-33036?
CVE-2026-33036 is a vulnerability with a CVSS score of 7.5 (HIGH). fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Versions 4.0.0-beta.3 through 5.5.5 contain a bypass vulnerability where numeric character refere...
How severe is CVE-2026-33036?
CVE-2026-33036 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-33036?
Check the references section above for vendor advisories and patch information. Affected products include: Naturalintelligence Fast-Xml-Parser.