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Review reviewCritical

CVE-2026-25896

NaturalIntelligence fast-xml-parser, Red Hat Advanced Cluster Security 4.8, Red Hat Advanced Cluster Security 4.9

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.

CVSS
9.3
EPSS
0.46%
37.8% percentile
CISA KEV
Not listed
Published
2026.02.21
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.46%
Technical severityCVSS 9.3

Vulnerability overview

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 product and versions

Product
NaturalIntelligence fast-xml-parser, Red Hat Advanced Cluster Security 4.8, Red Hat Advanced Cluster Security 4.9
Affected versions
>= >= 5.0.0, < 5.3.5, >= >= 4.1.3, < 4.5.4, >= 4.1.3 < 5.3.5
Fixed versions
5.3.5

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that NaturalIntelligence fast-xml-parser, Red Hat Advanced Cluster Security 4.8, Red Hat Advanced Cluster Security 4.9 and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
CWE
CWE-185, CWE-79