Hono Middleware Bypass in serveStatic via Path Decoding

Executive Summary

Hono versions 4.12.4 to 4.13.10 have a middleware bypass vulnerability in the serveStatic function. The issue occurs because the path is decoded twice: once for routing and again for file resolution. Attackers exploit this by sending malformed percent-encoded paths that the router matches in encoded form, allowing access to static files without running authentication middleware.

Useful 0 Not Useful 0

Detection Guidance

To detect this vulnerability, check if your Hono application uses serveStatic middleware with authentication or other security checks on static file paths. Monitor for requests with double-encoded paths or unusual percent-encoded sequences in URLs. Review server logs for attempts to access static files without triggering middleware.

Useful 0 Not Useful 0

Impact Analysis

Unauthenticated attackers could bypass security checks like authentication and access sensitive static files served by the application. This could lead to unauthorized data exposure or manipulation of static resources. Systems using affected Hono versions and mounting middleware on static paths are at risk.

Useful 0 Not Useful 0

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations may face compliance violations if static files containing personal or health information are exposed due to the middleware bypass.

Useful 0 Not Useful 0

Mitigation Strategies

Immediately upgrade Hono to version 4.13.11 or later to patch the vulnerability. If upgrading is not possible, disable serveStatic middleware or remove any authentication bypass risks by ensuring middleware runs before static file access. Review and restrict access to static file directories.

Useful 0 Not Useful 0