# CVE-2026-126066: fast-xml-parser: Quadratic CPU consumption scanning unterminated stop-node tags

Source: https://junglewise.ai/threats/cve-2026-126066-fast-xml-parser-allows-users-to-process-xml-from-js-object  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-10  
License: CC BY 4.0 with a link back

CVE-2026-126066 · Severity: low · CVSS 3.7 · Published 2026-11-10

fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Prior to 5.12.0, when the non-default stopNodes option is enabled, readStopNodeData() in OrderedObjParser.js calls readTagExp() for each less-than character in an unterminated stop-node body and repeatedly rescans the remaining input while looking for a closing greater-than character. An attacker who supplies XML containing many tag fragments without a later closing character can cause quadratic rescanning before parsing fails, blocking a Node.js event loop and causing CPU-exhaustion denial of service. This issue is fixed in version 5.12.0.

Technologies: [fast-xml-parser (npm)](https://junglewise.ai/threats/technologies/fast-xml-parser). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-126066 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126066 being exploited in the wild.

**How severe is CVE-2026-126066?** Low severity, with a CVSS score of 3.7, published 10 November 2026.

**Which products and versions are affected?** fast-xml-parser (npm) <= 5.11.2, SEMVER:introduced=0,fixed=5.12.0.

**Is there a fix for CVE-2026-126066?** Yes. fast-xml-parser (npm): upgrade to 5.12.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-126066?** 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 5.12.0 or later

  ```sh
  npm install fast-xml-parser@5.12.0
  ```


## Affected products

- fast-xml-parser (npm) <= 5.11.2, SEMVER:introduced=0,fixed=5.12.0

## Identifiers

- CVE-2026-126066
- GHSA-474x-hrwr-fgx4

## Related threats

- [fast-xml-parser DOCTYPE reset entity expansion limits bypass](https://junglewise.ai/threats/cve-2026-73569-fast-xml-parser-doctype-reset-entity-expansion-limits-bypass)
- [NaturalIntelligence fast-xml-parser XML injection in XMLBuilder](https://junglewise.ai/threats/cve-2026-41650-naturalintelligence-fast-xml-parser-xml-injection-in-xmlbuilder)
- [fast-xml-parser entity expansion bypass via falsy zero check](https://junglewise.ai/threats/cve-2026-33349-fast-xml-parser-entity-expansion-bypass-via-falsy-zero-check)
- [fast-xml-parser numeric entity expansion bypass](https://junglewise.ai/threats/cve-2026-33036-fast-xml-parser-numeric-entity-expansion-bypass)
- [NaturalIntelligence fast-xml-parser stack overflow in XMLBuilder](https://junglewise.ai/threats/cve-2026-27942-naturalintelligence-fast-xml-parser-stack-overflow-in-xmlbuilder)