fast-xml-parser: Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation
Summary
fast-xml-parser: Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation
Original description
The description as published by the source.
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.
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-33349 node-webfont
- Ubuntu UBUNTU-CVE-2026-33349 node-webfont
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov
- patch github.com