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

Status: published. Published: 2026-11-10. Updated: 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.

## Remediation

- fix: fast-xml-parser (npm): OSV reports a fixed version 5.12.0. Check the advisory for supported release branches. (source: OSV GHSA-474x-hrwr-fgx4) — https://github.com/advisories/GHSA-474x-hrwr-fgx4

## Affected products and versions

- NaturalIntelligence / fast-xml-parser: < 5.12.0 (affected). Source: CNA: GitHub_M
-  / fast-xml-parser (fast-xml-parser): ≥ 0; < 5.12.0 (affected, semver); OSV events: introduced 0; fixed 5.12.0. Source: OSV GHSA-474x-hrwr-fgx4

## Severity and prioritization

- CVSS 3.1: 3.7 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-407

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-474x-hrwr-fgx4 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/NaturalIntelligence/fast-xml-parser/commit/0c3659348364959da62954b73728fb3bd05ebcb4 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.12.0 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/advisories/GHSA-474x-hrwr-fgx4 (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-474x-hrwr-fgx4 (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-126066; retrieved 2026-11-10; source updated 2026-11-10

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-474x-hrwr-fgx4; retrieved 2026-11-10; source updated 2026-11-10

Revision: c83274e385475c08d27180c4004bfa423578669f2302e2e3433b423c3601435e

Canonical: https://y2.dev/cve/CVE-2026-126066

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