Critical [CVE-2026-73501] 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/validation_handler.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.

This vulnerability allows a remote attacker to bypass authentication checks. Specifically, the system incorrectly handles missing authentication configurations, substituting them with a function that does not verify user credentials.

This enables unauthorized access to protected resources that should require proper authentication, compromising the application's security.

Red Hat rates this as Important rather than Critical because exploitation requires the target application to explicitly instantiate and load the ValidationHandler middleware instead of ValidateRequest() or the Validator middleware.