A vulnerability in the Hono web framework allows unauthenticated attackers to bypass security middleware, potentially exposing sensitive static resources.

The flaw stems from inconsistent URL decoding between the router and the serveStatic utility. By using encoded slashes in a request, an unauthenticated attacker can circumvent route-based middleware protections to access protected files.

Successful exploitation allows unauthorized access to sensitive files or administrative endpoints that were intended to be protected by middleware. Given the CVSS score of 7.5, this high-severity vulnerability could lead to significant data breaches or unauthorized system information disclosure, directly impacting the confidentiality of the application.

Immediate Action: Update the Hono package to version 4.12.4 or later via the appropriate package manager (npm).

Proactive Monitoring: Review web server and application access logs for unusual patterns, specifically monitoring for URI strings containing encoded slashes (such as %2F) targeting protected paths.

Compensating Controls: Implement a Web Application Firewall (WAF) rule to block or normalize incoming requests containing double-encoded or suspicious URL-encoded characters before they reach the application layer.

Public Exploit Available: No (exploit_available: false)

This vulnerability presents a clear risk to any application relying on Hono for route-based access control. Organizations should prioritize updating to version 4.12.4 immediately to resolve the inconsistency in URL decoding. Failure to patch may result in the exposure of sensitive data that is otherwise protected by application-level middleware.