CVE-2026-26278 — fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)

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. In versions 4.1.3 through 5.3.5, the XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application. Version 5.3.6 fixes the issue. As a workaround, avoid using DOCTYPE parsing by `processEntities: false` option.

Affected (CNA)

Vendor / product	Versions
NaturalIntelligence / fast-xml-parser	affected >= 5.0.0, < 5.3.6; affected >= 4.1.3, < 4.5.4

CWE

CWE-776

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

redhat-SADP

A denial of service flaw was found in fast-xml-parser. A remote attacker can exploit this vulnerability by providing a specially crafted, small XML input. This input can force the XML parser to perform an unlimited amount of entity expansion, consuming excessive resources. This can lead to the application freezing for an extended period, resulting in a Denial of Service (DoS).