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

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). 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
    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

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