CVE-2026-25896 PUBLISHED

fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names

Assigner: GitHub_M
Reserved: 06.02.2026 Published: 20.02.2026 Updated: 20.02.2026

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. From 4.1.3to before 5.3.5, a dot (.) in a DOCTYPE entity name is treated as a regex wildcard during entity replacement, allowing an attacker to shadow built-in XML entities (<, >, &, ", ') with arbitrary values. This bypasses entity encoding and leads to XSS when parsed output is rendered. This vulnerability is fixed in 5.3.5.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
CVSS Score: 9.3

Product Status

Vendor NaturalIntelligence
Product fast-xml-parser
Versions
  • Version >= 4.1.3, < 5.3.5 is affected

References

Problem Types

  • CWE-185: Incorrect Regular Expression CWE