CVE-2026-25896
fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names
HIGH 7.1EPSS 0.6%
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.
- Affected
- NaturalIntelligence · fast-xml-parser
- CVSS v3.1 CNA
- 7.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L - CVSS v3.1 GITHUB
- 9.3 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N - EPSS
- 0.57% chance of exploitation in the next 30 days, 46th percentile
- Published
- 2026-02-20
- Updated
- 2026-09-10
Proof-of-concept exploits (1)
Security advisories
- NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-m7jm-9gc2-mpf2
- NaturalIntelligence/fast-xml-parser/commit/943ef0eb1b2d3284e72dd74f44a042ee9f07026e