Description
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 products
naturalintelligence: fast-xml-parser
References10
- github.com/NaturalIntelligence/fast-xml-parser/security/advisor… ExploitMitigationVendor Advisory
- github.com/NaturalIntelligence/fast-xml-parser/commit/943ef0eb1… Patch
- github.com/NaturalIntelligence/fast-xml-parser/commit/ddcd0acf2… Patch
- github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.… ProductRelease Notes
- access.redhat.com/errata/RHSA-2026:40984
- access.redhat.com/errata/RHSA-2026:41941
- access.redhat.com/errata/RHSA-2026:41944
- access.redhat.com/errata/RHSA-2026:51349
- access.redhat.com/errata/RHSA-2026:6174
- access.redhat.com/errata/RHSA-2026:6802
Metrics
- CVSS 3.1
-
9.3
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N - EPSS — exploit probability
- 1% percentile: 45 · as of 12 November 2026
- CWE
- CWE-185CWE-79
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