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High severityNVD Advisory· Published Mar 20, 2026· Updated Mar 25, 2026

fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)

CVE-2026-33036

Description

fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Versions 4.0.0-beta.3 through 5.5.5 contain a bypass vulnerability where numeric character references (&#NNN;, &#xHH;) and standard XML entities completely evade the entity expansion limits (e.g., maxTotalExpansions, maxExpandedLength) added to fix CVE-2026-26278, enabling XML entity expansion Denial of Service. The root cause is that replaceEntitiesValue() in OrderedObjParser.js only enforces expansion counting on DOCTYPE-defined entities while the lastEntities loop handling numeric/standard entities performs no counting at all. An attacker supplying 1M numeric entity references like A can force ~147MB of memory allocation and heavy CPU usage, potentially crashing the process—even when developers have configured strict limits. This issue has been fixed in version 5.5.6.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
fast-xml-parsernpm
>= 5.0.0, < 5.5.65.5.6
fast-xml-parsernpm
>= 4.0.0-beta.3, < 4.5.54.5.5

Affected products

33

Patches

Vulnerability mechanics

References

6

News mentions

0

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