Authorization Bypass in DeepTutor via MCP Tools

Executive Summary

DeepTutor before version 1.4.10 contains an authorization bypass vulnerability that allows low-privilege users to invoke unrestricted MCP tools.

This happens because the allowed_mcp_tools function returns None instead of denying access when the mcp_tools grant is missing for a user.

As a result, attackers or malicious prompt-injected content within a user session can enumerate and invoke any configured MCP tool, including filesystem, shell, and browser servers.

This leads to unauthorized access to sensitive deployment resources.

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Detection Guidance

This vulnerability involves unauthorized access to MCP tools by non-admin users due to improper authorization checks in DeepTutor versions before 1.4.10.

To detect exploitation attempts or presence of this vulnerability on your system, you can monitor for unusual invocation or enumeration of MCP tools by low-privilege users.

Suggested detection approaches include:

• Review application logs for calls to MCP tools initiated by non-admin users.
• Check for unexpected shell, filesystem, or browser server commands executed within user sessions.
• Use network monitoring tools to detect unusual traffic patterns or commands targeting MCP tool endpoints.

Specific commands depend on your environment and logging setup, but examples include:

• Using grep or similar tools to search DeepTutor logs for MCP tool invocations by non-admin users, e.g., `grep 'mcp_tool' /var/log/deeptutor/*.log`.
• Monitoring active user sessions for shell or filesystem commands that should be restricted.
• Network packet capture tools like tcpdump or Wireshark to inspect traffic for unauthorized MCP tool usage.

Since the vulnerability arises from missing or incorrect grant configurations, auditing user grants for the presence or absence of the `mcp_tools` grant can also help detect vulnerable setups.

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Impact Analysis

This vulnerability allows non-admin users or attackers acting within a user session to gain unauthorized access to sensitive backend capabilities.

• They can invoke MCP tools such as filesystem, shell, and browser servers without proper authorization.
• This can lead to unauthorized enumeration and execution of critical tools, potentially compromising sensitive deployment resources.

Such unauthorized access can result in data breaches, system manipulation, or other security incidents.

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Compliance Impact

The vulnerability allows unauthorized access to sensitive deployment resources by enabling low-privilege users to invoke unrestricted MCP tools, including filesystem, shell, and browser servers. This unauthorized access could lead to exposure or manipulation of sensitive data.

Such unauthorized access and potential data exposure can negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require strict access controls and protection of sensitive information.

The fix introduced in version 1.4.10 enforces a deny-by-default policy for MCP tools for non-admin users, requiring explicit administrative grants to access these tools, thereby helping to restore compliance with access control requirements.

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Mitigation Strategies

To mitigate the authorization bypass vulnerability in DeepTutor before version 1.4.10, you should upgrade to version 1.4.10 or later, where the issue is fixed.

The fix introduces a deny-by-default mechanism for MCP tools for non-admin users, requiring administrators to explicitly grant access to specific MCP tools.

• Upgrade DeepTutor to version 1.4.10 or later.
• Review and explicitly grant MCP tool access only to trusted non-admin users.
• Ensure that non-admin users without explicit MCP tool grants are denied access by default.
• Verify that admin users retain unrestricted access as intended.

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