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9.3Critical

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.

What this means for your business

  • It affects Naturalintelligence Fast-Xml-Parser. It matters if your company, or a supplier that handles your data, runs it.
  • Code showing how to exploit it has been published, but real attacks have not been confirmed.
  • An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
  • FIRST's prediction model gives it a 0.5% chance of attack attempts being seen in the next 30 days, ranking above 38% of all known flaws.

What to do

  1. 1Check whether your company or your suppliers run Naturalintelligence Fast-Xml-Parser, and which version. The affected versions are listed further down this page.
  2. 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

Check if you’re exposedBook a call

Scoring

CVSS
9.3 (v3.1)
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
Weakness
CWE-185
Assigned by
security-advisories@github.com

Dates

Published
2026-02-20
Last modified
2026-09-10
Sources
NVD

Affected products

  • Naturalintelligence Fast-Xml-Parser4.1.3 - 5.3.5

As listed in the NVD configuration data. Not a statement about your estate.

References