CVE-2026-47673

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.

Details

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:

• Bypass of network-layer security controls that inspect or filter requests based on the authorization scheme identifier
• Token reuse across authentication schemes in applications that use multiple authorization mechanisms

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

CVE-2026-47673 has a CVSS score of 4.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.12.21); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-47673? CVE-2026-47673 is a medium-severity security vulnerability in hono (npm), affecting versions < 4.12.21. It is fixed in 4.12.21.
2. How severe is CVE-2026-47673? CVE-2026-47673 has a CVSS score of 4.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of hono are affected by CVE-2026-47673? hono (npm) versions < 4.12.21 is affected.
4. Is there a fix for CVE-2026-47673? Yes. CVE-2026-47673 is fixed in 4.12.21. Upgrade to this version or later.
5. Is CVE-2026-47673 exploitable, and should I be worried? Whether CVE-2026-47673 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-47673 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-47673? Upgrade hono to 4.12.21 or later.