The jwt and jwk middlewares do not verify that the Authorization header value uses theBearer scheme. Any two-part header value — regardless of the scheme name in the first position — proceeds to JWT verification. A request presenting a valid JWT under a non-Bearer scheme identifier (such as Basic or Token) is authenticated identically to a correctly formed Bearer request.

When processing an Authorization (or custom) header, the middleware splits the value on whitespace and uses the second token as the JWT to verify. It does not check that the first token is bearer (case-insensitively). RFC 6750 specifies that JWT bearer tokens must be presented using the Bearer scheme; other scheme identifiers carry distinct semantics and may be subject to different policies in network-layer security controls.

This discrepancy means that scheme-aware external controls — such as WAF rules, API gateways, or reverse proxies that apply policies specific to the Bearer scheme identifier — can be bypassed by presenting a valid JWT under a different scheme name.

This issue affects hono/jwt and hono/jwk middleware.

An attacker who possesses a valid JWT may present it under a non-Bearer scheme identifier and still pass middleware authentication.

This may lead to:

This issue affects applications where hono/jwt or hono/jwk authentication is combined with external controls that enforce scheme-based access policies.