XSS in Naturalintelligence Fast-Xml-Parser
CVE-2026-25896
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.3 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N.
EPSS exploit prediction
EPSS: 0.006 (46.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 46th percentile — 46.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.006 · change: +0.001
Affected products
- Naturalintelligence Fast-Xml-Parser — versions >= 5.0.0, < 5.3.5, >= 4.1.3, < 4.5.4
Weakness classification (CWE)
References
- github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-m7jm-9g… (Exploit, Mitigation, Vendor Advisory)
- github.com/NaturalIntelligence/fast-xml-parser/commit/943ef0eb1b2d3284e72dd74f4… (Patch)
- github.com/NaturalIntelligence/fast-xml-parser/commit/ddcd0acf26ddd682cb0dc15a2… (Patch)
- github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.3.5 (Product, Release Notes)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-25896?
- CVE-2026-25896 is a critical-severity vulnerability in Naturalintelligence Fast-Xml-Parser, classified under Incorrect Regular Expression. CVSS score: 9.3/10. Published 2026-02-20.
- How severe is CVE-2026-25896?
- Critical severity. CVSS v3 base score is 9.3 out of 10.