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CVE-2026-73569 — fast-xml-parser

Fix: NaturalIntelligence/fast-xml-parser@4e546e0

CVE-2026-73569 is a CWE-776 vulnerability in fast-xml-parser. A fix is available for fast-xml-parser — see the affected versions and patch details below.

fast-xml-parser: Repeated DOCTYPE declarations reset entity expansion limits

Also known asGHSA-8r6m-32jq-jx6q
Published
Aug 13, 2026
Updated
Sep 20, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Sep 28, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-73569.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

5Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream
fast-xml-parsernpm
91.3Mdownloads / week

Description

Impact

fast-xml-parser processes multiple "DOCTYPE" declarations within a single XML document. Each declaration passes its entities to @nodable/entities through addInputEntities().

addInputEntities() resets the entity expansion counters every time it is called. An attacker can therefore insert additional DOCTYPE declarations to repeatedly reset maxTotalExpansions and maxExpandedLength during one parse operation.

This allows a crafted XML document to exceed the configured entity-expansion limits and can cause excessive CPU use, event-loop blocking, memory exhaustion, and process termination.

Workarounds

  • Manually check if multiple DOCTYPEs are not present in input contents
  • Update to v5.10.1
  • Keep processEntity flag off

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmfast-xml-parser≥ 5.9.3&&< 5.10.15.10.1npm install fast-xml-parser@5.10.1

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fast-xml-parser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update fast-xml-parser to 5.10.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-73569 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This is an Important denial of service vulnerability affecting Red Hat products that process untrusted XML input using the `fast-xml-parser` library versions 5.9.3 through 5.10.0. A remote attacker could provide a specially crafted XML document with multiple DOCTYPE declarations, leading to excessive CPU usage, memory…

Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Source: Red Hat security advisory for CVE-2026-73569 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Ansible Automation Platform 2.2ansible-automation-platform/bootc-automation-portal-rhel9:1788943531RHSA-2026:66003
Red Hat Migration Toolkit for Applications 8.2mta/mta-ui-rhel9:1789446780RHSA-2026:67724
Red Hat Openshift Data Foundation 4.22odf4/cephcsi-rhel9:1788162216RHSA-2026:65130

Frequently Asked Questions

### Impact `fast-xml-parser` processes multiple "DOCTYPE" declarations within a single XML document. Each declaration passes its entities to `@nodable/entities` through `addInputEntities()`. `addInputEntities()` resets the entity expansion counters every time it is called. An attacker can therefore insert additional DOCTYPE declarations to repeatedly reset maxTotalExpansions and maxExpandedLength during one parse operation. This allows a crafted XML document to exceed the configured entity-expansion limits and can cause excessive CPU use, event-loop blocking, memory exhaustion, and process t
O3 Security · Impact-Aware SCA

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CVE-2026-73569: fast-xml-parser | O3 Security