Is CVE-2026-33036 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-33036 being exploited in the wild.

How severe is CVE-2026-33036?

Low severity, with a CVSS score of 3.1, published 17 March 2026.

Which products and versions are affected?

fast-xml-parser (npm) SEMVER:introduced=5.0.0,fixed=5.5.6.

Is there a fix for CVE-2026-33036?

Yes. fast-xml-parser (npm): upgrade to 5.5.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-33036 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-33036?

Check whether you run fast-xml-parser (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-33036: fast-xml-parser numeric entity expansion bypass

CVE-2026-33036 · Severity: low · CVSS 3.1 · Published 2026-03-17

fast-xml-parser is a widely-used JavaScript library for parsing and processing XML documents. The library contains a flaw where numeric entity references (such as A) bypass configured entity expansion limits, allowing attackers to trigger denial of service through excessive memory and CPU consumption. An application developer believing they are protected by strict entity limits can still be compromised.

Technologies: fast-xml-parser (npm). Vendors: npm.

Quick answers

Is CVE-2026-33036 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-33036 being exploited in the wild.
How severe is CVE-2026-33036?: Low severity, with a CVSS score of 3.1, published 17 March 2026.
Which products and versions are affected?: fast-xml-parser (npm) SEMVER:introduced=5.0.0,fixed=5.5.6.
Is there a fix for CVE-2026-33036?: Yes. fast-xml-parser (npm): upgrade to 5.5.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-33036 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-33036?: Check whether you run fast-xml-parser (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

fast-xml-parser (npm): upgrade to 5.5.6 or later
```
npm install fast-xml-parser@5.5.6
```

Technical details

The vulnerability is a CWE-776 XML Entity Expansion Denial of Service. The root cause is incomplete remediation of CVE-2026-26278: the replaceEntitiesValue() function in OrderedObjParser.js tracks entity expansion for DOCTYPE-defined entities but not for numeric character references (&#NNN; and &#xHH;) or standard XML entities, which are processed through a separate code path. An attacker who can provide XML input can craft documents with massive numbers of numeric entity references—100,000 references produce 500,000 characters despite maxExpandedLength=100, and 1M references consume ~147MB. Network vector, no authentication required. Patches available in versions 4.5.5 and 5.5.6.

Affected products

NaturalIntelligence fast-xml-parser >=4.0.0-beta.3, <=5.5.5

Identifiers

CVE-2026-33036
GHSA-8gc5-j5rx-235r

Timeline

2026-03-17: disclosed
2026-03-17: patched: versions 4.5.5 and 5.5.6

References

https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-8gc5-j5rx-235r

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