---
title: "CVE-2026-25896: fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names"
url: https://erroneo.us/security/cve/CVE-2026-25896/
description: "CVE-2026-25896 (fast-xml-parser (npm)): fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-02-20
date_modified: 2026-09-10
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-25896"
kev: false
cvss: 9.3
epss: 0.00571
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.6% , percentile 46: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 46% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes fast-xml-parser (npm) >= 5.0.0, < 5.3.5, fixed in 5.3.5 ; fast-xml-parser (npm) >= 4.1.3, < 4.5.4, fixed in 4.5.4 . Check your lockfile, including transitive dependencies.

## What it is

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 (&lt;, &gt;, &amp;, &quot;, &apos;) 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 packages

- npm `fast-xml-parser` >= 5.0.0, < 5.3.5 → fixed: 5.3.5
- npm `fast-xml-parser` >= 4.1.3, < 4.5.4 → fixed: 4.5.4

## Affected products (CVE record)

- NaturalIntelligence fast-xml-parser: >= 5.0.0, < 5.3.5, >= 4.1.3, < 4.5.4

## Severity

- GitHub_M CVSS 3.1: 9.3 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N`
- redhat-SADP CVSS 3.1: 7.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L`
- GitHub CVSS 3.1: 9.3 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.57% probability of exploitation activity in the next 30 days; percentile 46.

## Sources

- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:7110)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:7128)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:6174)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:6802)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:41941)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:41944)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:40984)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:51349)
- [GitHub Advisory GHSA-m7jm-9gc2-mpf2](https://github.com/advisories/GHSA-m7jm-9gc2-mpf2)
- [CVE.org record CVE-2026-25896](https://www.cve.org/CVERecord?id=CVE-2026-25896)
- [NVD entry CVE-2026-25896](https://nvd.nist.gov/vuln/detail/CVE-2026-25896)
- [github.com](https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-m7jm-9gc2-mpf2)
- [github.com](https://github.com/NaturalIntelligence/fast-xml-parser/commit/943ef0eb1b2d3284e72dd74f44a042ee9f07026e)
- [github.com](https://github.com/NaturalIntelligence/fast-xml-parser/commit/ddcd0acf26ddd682cb0dc15a2bd6aa3b96bb1e69)
- [github.com](https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.3.5)
- [access.redhat.com](https://access.redhat.com/security/cve/CVE-2026-25896)
- [RHBZ#2441501](https://bugzilla.redhat.com/show_bug.cgi?id=2441501)
- [security.access.redhat.com](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-25896.json)

---
Source page: https://erroneo.us/security/cve/CVE-2026-25896/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt