CVE-2026-25896 — fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names

Description (CNA)

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 (CNA)

Vendor / product	Versions
NaturalIntelligence / fast-xml-parser	affected >= 5.0.0, < 5.3.5; affected >= 4.1.3, < 4.5.4

CWE

CWE-185

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

redhat-SADP

A flaw was found in fast-xml-parser. A remote attacker can exploit this vulnerability by providing a specially crafted XML input. The system incorrectly interprets a dot in a DOCTYPE entity name as a regular expression wildcard during processing. This allows the attacker to bypass security measures and inject malicious scripts, resulting in Cross-Site Scripting (XSS) when the parsed output is displayed to users.