JWT Algorithm Confusion Vulnerability in Hono JWT Middleware

Executive Summary

This vulnerability in Hono's JWT verification middleware allowed the JWT header's 'alg' value to influence signature verification when the selected JWK did not explicitly specify an algorithm. This could lead to JWT algorithm confusion, potentially allowing forged tokens to be accepted. The fix requires the 'alg' option to be explicitly specified to prevent this confusion.

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Impact Analysis

This vulnerability can allow attackers to forge JWT tokens that are accepted as valid by the application, potentially leading to unauthorized access or privilege escalation.

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Mitigation Strategies

Upgrade Hono to version 4.11.4 or later, as this version includes a fix that requires the alg option to be explicitly specified in the JWT middleware, preventing algorithm confusion and acceptance of forged tokens.

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Detection Guidance

To detect this vulnerability, you should check if your Hono JWT middleware configuration explicitly specifies the 'alg' parameter in the JWT verification options. Vulnerable versions prior to 4.11.4 do not require this parameter, allowing algorithm confusion attacks. You can audit your application code for usage of the jwt middleware and verify if 'alg' is set. For example, look for code like `app.use('/auth/*', jwt({ secret: 'your-secret' }))` which is vulnerable, versus the fixed usage `app.use('/auth/*', jwt({ secret: 'your-secret', alg: 'HS256' }))`. Additionally, monitoring JWT tokens in your network traffic for unexpected or mismatched 'alg' header values could indicate exploitation attempts. There are no specific commands provided in the resources, but code inspection and configuration review are recommended detection methods. [2, 1]

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