XML Entity Expansion in fast-xml-parser - CVE-2026-33036
Published: April 20, 2026
Vulnerability identifier: #VU126615
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-33036
CWE-ID: CWE-776
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Natural Intelligence
Affected software:
fast-xml-parser
fast-xml-parser
Detailed vulnerability description
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to improper restriction of entity expansion in replaceEntitiesValue() in src/xmlparser/OrderedObjParser.js when parsing XML input containing numeric character references or standard XML entities. A remote attacker can send specially crafted XML input with massive numbers of numeric entity references to cause a denial of service.
The configured entity expansion limits are enforced only for DOCTYPE-defined entities, while numeric character references and standard XML entities are processed through a separate code path without expansion counting.
How to mitigate CVE-2026-33036
Install security update from vendor's website.