Hono CORS Middleware Vary Header Reflection Vulnerability

Executive Summary

This vulnerability exists in Hono versions before 4.10.2 and is fixed in 4.10.3. It is related to the CORS middleware, which incorrectly handles the Vary header. When the origin is not set to "*", the middleware copies the Vary header from the incoming request into the response. Since the Vary header is a response header that should be controlled by the server, an attacker can supply arbitrary Vary values that get reflected in the response.

This flaw can lead to cache key pollution and inconsistent enforcement of CORS policies, especially in environments that use shared caches or proxies.

Useful 0 Not Useful 0

Detection Guidance

To detect this vulnerability on your network or system, you can monitor HTTP responses from Hono servers for unexpected or attacker-controlled Vary headers when the Origin header is not set to "*".

One approach is to send HTTP requests with custom Vary headers and observe if those headers are reflected in the response, indicating the vulnerable middleware behavior.

Example commands using curl to test for this vulnerability:

• curl -i -H "Origin: http://example.com" -H "Vary: X-Custom-Test" http://target-hono-server/
• Check the response headers for the presence of the injected "Vary: X-Custom-Test" header. If it appears, the server is likely vulnerable.

Additionally, monitoring logs or using network inspection tools to detect unusual or unexpected Vary headers in responses from Hono servers before version 4.10.3 can help identify exploitation attempts or presence of the vulnerability.

Useful 0 Not Useful 0

Impact Analysis

The vulnerability can cause cache key pollution, meaning that attackers can manipulate cache behavior by injecting arbitrary Vary header values. This can result in inconsistent CORS enforcement, potentially allowing unauthorized cross-origin requests to succeed or legitimate requests to be blocked incorrectly.

In environments relying on shared caches or proxies, this inconsistency can lead to security risks such as data leakage or unauthorized access due to improper CORS policy enforcement.

Useful 0 Not Useful 0

Compliance Impact

This vulnerability in Hono's CORS middleware can lead to cache key pollution and inconsistent CORS enforcement in environments using shared caches or proxies. Such issues may increase the risk of unauthorized data exposure or access control failures.

While the CVE description does not explicitly mention compliance with standards like GDPR or HIPAA, the potential for inconsistent access control and data exposure could negatively impact compliance with these regulations, which require strict controls on data privacy and security.

Useful 0 Not Useful 0

Mitigation Strategies

To mitigate this vulnerability, upgrade Hono to version 4.10.3 or later, where the flaw in the CORS middleware has been fixed.

Useful 0 Not Useful 0