Executive Summary

This vulnerability is an authentication bypass in the Rowboat project's tools_webhook component, specifically in the file apps/experimental/tools_webhook/app.py. It arises because the application improperly verifies JSON Web Token (JWT) signatures by trusting the algorithm (alg) header provided by the client.

An attacker can exploit this by specifying the algorithm as "none" in the JWT header, which causes the server to skip signature verification entirely. This allows the attacker to forge tokens without a valid cryptographic signature.

As a result, the attacker can impersonate any user or service, gaining unauthorized access and the ability to execute arbitrary tool commands within the Rowboat environment, effectively bypassing authentication on the /tool_call endpoint.

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Detection Guidance

This vulnerability can be detected by attempting to exploit the improper JWT signature verification on the /tool_call endpoint of the Rowboat tools webhook service. Specifically, you can test if the service accepts JWT tokens with the "alg" header set to "none", which should normally be rejected.

A practical detection method is to send a crafted POST request with a forged JWT token in the X-Tools-JWE HTTP header using the "none" algorithm and observe if the server accepts it and returns HTTP 200 OK.

Example command to test the vulnerability:

• curl -i -X POST http://127.0.0.1:5000/tool_call \
• -H "Content-Type: application/json" \
• -H "X-Tools-JWE: eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.e30.signature" \
• -d '{"content": "jwe_exploit_test"}'

If the server accepts this request and processes it successfully, it indicates the presence of the vulnerability.

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Mitigation Strategies

Immediate mitigation steps involve fixing the JWT signature verification logic to reject tokens that specify the "none" algorithm and only accept secure algorithms.

• Implement algorithm whitelisting by allowing only secure algorithms such as HS256 or RS256.
• Explicitly reject tokens where the "alg" field is set to "none" or any case variation.

An example of secure token decoding using the PyJWT library is:

• import jwt
• try:
• decoded_token = jwt.decode(token, SECRET_KEY, algorithms=["HS256"])
• except jwt.InvalidTokenError:
• return "Unauthorized", 401

These steps will prevent attackers from bypassing authentication by forging tokens with the "none" algorithm.

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Compliance Impact

This vulnerability allows unauthenticated remote attackers to fully bypass authentication and gain administrative control over the Rowboat tools webhook service by exploiting improper JWT signature verification.

Such unauthorized access and control can lead to unauthorized data access, manipulation, or disclosure, which may result in non-compliance with common standards and regulations like GDPR and HIPAA that require strong authentication and protection of sensitive data.

The advisory references OWASP A02:2021 – Cryptographic Failures, highlighting the critical nature of cryptographic verification failures in security compliance contexts.

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Impact Analysis

This vulnerability allows remote attackers to fully bypass authentication and gain administrative control over the Rowboat tools webhook service.

• Attackers can impersonate any user or service by forging JWT tokens.
• They can execute arbitrary commands within the Rowboat environment.
• This leads to unauthorized access and potential compromise of the affected system.

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