fast-xml-parser: Repeated DOCTYPE declarations reset entity expansion limits
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
processEntityflag off
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | fast-xml-parser | >= 5.9.3, < 5.10.1 | 5.10.1 |
References
- https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-8r6m-32jq-jx6q
- https://github.com/NaturalIntelligence/fast-xml-parser/commit/4e546e03987662de5495d050b5fba26bea65383f
- https://github.com/NaturalIntelligence/fast-xml-parser
- https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.10.1
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-776- Platform
- npm
- Package
fast-xml-parser- Disclosed
- 21.07.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-8r6m-32jq-jx6q - CC BY 4.0
Vulnerability history: fast-xml-parser
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 12
- First → latest
- 08.2021 07.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 6
- Medium 3
- Low 2
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 2
- 2024: 1
- 2025: 0
- 2026: 8
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fast-xml-parser: Repeated DOCTYPE declarations reset entity expansion limits this entry
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