CVE-2026-33349
fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks.
Does this matter?
Lower severity and a low EPSS score (0.45%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 5.9 MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.45% probability · 38th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-1284
- Affected
- naturalintelligence/fast-xml-parser
- Source
- security-advisories@github.com
References
- https://github.com/NaturalIntelligence/fast-xml-parser/commit/239b64aa1fc5c5455ddebbbb54a187eb68c9fdb7Patch
- https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-jp2q-39xq-3w4gExploit, Mitigation, Vendor Advisory
- https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-jp2q-39xq-3w4gExploit, Mitigation, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.