fast-xml-parser: Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation (NaturalIntelligence fast-xml-parser)
At a glance
- Source
- NVD
- EPSS
- EPSS 0.47 % · percentile 40 ()
- State
- PUBLISHED
- Published
- Updated
- Assigner
- GitHub_M
- NVD status
- Analyzed
Description
fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. From version 4.0.0-beta.3 to before version 5.5.7, the DocTypeReader in fast-xml-parser uses JavaScript truthy checks to evaluate maxEntityCount and maxEntitySize configuration limits. When a developer explicitly sets either limit to 0 — intending to disallow all entities or restrict entity size to zero bytes — the falsy nature of 0 in JavaScript causes the guard conditions to short-circuit, completely bypassing the limits. An attacker who can supply XML input to such an application can trigger unbounded entity expansion, leading to memory exhaustion and denial of service. This issue has been patched in version 5.5.7.
Weaknesses (CWE)
- CWE-1284 — Improper Validation of Specified Quantity in Input
References
Scores
| Version | Score | Vector | Scored by |
|---|---|---|---|
| CVSS 3.1 | MEDIUM 5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H | GitHub_M |
| CVSS 3.1 | MEDIUM 5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H | NVD · security-advisories@github.com (Secondary) |
Advisories
- GHSA-jp2q-39xq-3w4g — Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation in fast-xml-parser
European references
- ENISA EUVD · EUVD-2026-20080
- GCVE · GCVE-0-2026-33349
CERT-FR advisories
- CERTFR-2026-AVI-0667 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
Affected configurations (NVD CPE)
cpe:2.3:a:naturalintelligence:fast-xml-parser:*:*:*:*:*:*:*:*≥ 4.0.1 < 4.5.5cpe:2.3:a:naturalintelligence:fast-xml-parser:*:*:*:*:*:*:*:*≥ 5.0.0 < 5.5.7cpe:2.3:a:naturalintelligence:fast-xml-parser:4.0.0:-:*:*:*:*:*:*cpe:2.3:a:naturalintelligence:fast-xml-parser:4.0.0:beta3:*:*:*:*:*:*cpe:2.3:a:naturalintelligence:fast-xml-parser:4.0.0:beta4:*:*:*:*:*:*cpe:2.3:a:naturalintelligence:fast-xml-parser:4.0.0:beta5:*:*:*:*:*:*cpe:2.3:a:naturalintelligence:fast-xml-parser:4.0.0:beta6:*:*:*:*:*:*cpe:2.3:a:naturalintelligence:fast-xml-parser:4.0.0:beta7:*:*:*:*:*:*cpe:2.3:a:naturalintelligence:fast-xml-parser:4.0.0:beta8:*:*:*:*:*:*
Affected products
| Product | Versions |
|---|---|
| NaturalIntelligence · fast-xml-parser | affected >= 4.0.0-beta.3, < 5.5.7 |
Sources
| Source | Licence |
|---|---|
| CVE List (CVEProject cvelistV5) | CVE Program Terms of Use |
| EPSS (FIRST.org) | FIRST — attribution requested |
| ENISA EUVD | ENISA — reproduction authorised, source acknowledged |
| CERT-FR (ANSSI) | Licence Ouverte / Etalab 2.0 |
| NVD (NIST) via fkie-cad/nvd-json-data-feeds | Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD |