fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)

Description

The XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application.

Recommendation

Update the fast-xml-parser package to the latest compatible version. Followings are version details:

• Affected version(s): **>= 5.0.0, < 5.3.6

  >= 4.1.3, < 4.5.4**

• Patched version(s): **5.3.6

  4.5.4**

References

• GHSA-jmr7-xgp7-cmfj
• CVE-2026-26278
• CWE-776
• CAPEC-310
• OWASP 2021-A5
• OWASP 2021-A6

Related Issues

• fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026- - CVE-2026-33036
• fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names - CVE-2026-25896
• Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation in fast-xml-parser - CVE-2026-33349
• fast-xml-parser has RangeError DoS Numeric Entities Bug - CVE-2026-25128

Tags:

npm

fast-xml-parser