CVE-2026-73501: kin-openapi: ValidationHandler.Load() Fail-Open Authentication Bypass via NoopAuthenticationFunc Default
kin-openapi is a Go project for handling OpenAPI files. Prior to 0.144.0, ValidationHandler.Load() in openapi3filter/validationhandler.go silently replaces a nil AuthenticationFunc with NoopAuthenticationFunc, which returns nil without checking credentials. This substitution causes every OpenAPI security requirement to be satisfied for unauthenticated requests when an application relies on ValidationHandler as its enforcement middleware. The no-op callback prevents the fail-closed ErrAuthenticationServiceMissing path from being reached and forwards the request to protected handlers that may require an API key, OAuth token, or another security scheme. This issue is fixed in version 0.144.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
kin-openapito a version that resolves this vulnerability.Fixed in 0.144.0
Event History
Frequently Asked Questions
What is the severity of CVE-2026-73501?
CVE-2026-73501 has a severity rating of critical, with a score of 9.1.
How do I fix CVE-2026-73501?
To mitigate CVE-2026-73501, upgrade kin-openapi to version 0.144.0 or higher.
What causes CVE-2026-73501?
CVE-2026-73501 is caused by the ValidationHandler.Load() method replacing a nil AuthenticationFunc with NoopAuthenticationFunc, allowing for an authentication bypass.
Is CVE-2026-73501 exploitable?
Yes, CVE-2026-73501 is exploitable because it allows unauthenticated access to all OpenAPI specifications.
What versions of kin-openapi are affected by CVE-2026-73501?
CVE-2026-73501 affects all versions of kin-openapi prior to 0.144.0.