CVE-2026-58168: DeepTutor Authorization Bypass Allows Unrestricted MCP Tool Access

Technical summary

The vulnerability exists in deeptutor/multi_user/tool_access.py where the allowed_mcp_tools function returns None (permissive) rather than a denied result when mcp_tools is absent from a user's access grant. MCP tools, a model context protocol layer for tool execution, include filesystem, shell, and browser servers. The logic flaw creates a dangerous default-allow pattern: if an administrator omits mcp_tools from a user's grant configuration, the absence of an explicit denial is misinterpreted as blanket permission. An attacker with low privilege or through prompt injection within an existing session can enumerate available MCP tools and invoke them without restriction, bypassing the intended access control model.

Business impact

Exploitation could lead to unauthorized access to sensitive deployment resources, data exfiltration, system command execution, and lateral movement within infrastructure. Organizations running DeepTutor in multi-user environments face elevated risk of insider threats and prompt-injection attacks compromising confidential information, operational continuity, and compliance posture. The severity is heightened in cloud or shared-tenant deployments where isolation is critical.

Affected systems

DeepTutor versions before 1.4.10 are affected. The vulnerability requires an active user session or low-privilege account, so systems with multi-user access or those exposed to untrusted prompts are at highest risk. Single-user or air-gapped deployments have reduced attack surface but are not immune to prompt-injection vectors.

Exploitability

Exploitability is straightforward: a low-privilege user or prompt-injected content within a session can immediately enumerate and invoke MCP tools without authentication or authorization barriers. No user interaction beyond normal session activity is required. Network access is required to reach the DeepTutor instance. The attack requires existing user credentials or session hijacking, but once inside, the authorization bypass requires no additional complexity.

Remediation

Upgrade DeepTutor to version 1.4.10 or later, which corrects the allowed_mcp_tools function to return a denied result (rather than None) when mcp_tools is omitted from a user's grant. After patching, review all existing user access grants to ensure mcp_tools are explicitly configured per user role and principle of least privilege. Consider implementing additional controls such as MCP tool usage logging, prompt injection detection, and network segmentation between user-facing applications and sensitive backend tools.

Patch guidance

Update DeepTutor to version 1.4.10 or later. Verify the patch is applied by checking the version number in your deployment (typically available via the application's About page or API endpoint). Before patching production, test the update in a staging environment to ensure no breaking changes to existing user grants or tool configurations. After applying the patch, restart all DeepTutor instances and confirm that low-privilege users can no longer invoke tools not explicitly granted to them.

Detection guidance

Monitor logs for attempts to invoke MCP tools (filesystem, shell, browser servers) by accounts with restricted privileges or unusual tool invocation patterns. Search for Tool not allowed or permission denied errors followed by successful tool execution—this sequence indicates a potential bypass. Examine audit trails for users suddenly accessing tools they should not have permission for. Implement real-time alerting on unauthenticated or unauthorized MCP tool invocations. Check for prompt injection payloads attempting to enumerate or invoke tools via user input.

Why prioritize this

This is a HIGH-severity authorization bypass affecting confidentiality, integrity, and availability with a CVSS score of 8.8. The default-allow logic is particularly dangerous because misconfiguration becomes the common case rather than the exception. Low privileges required for exploitation and network accessibility make this a practical risk in most DeepTutor deployments. Prompt injection vectors in AI/LLM contexts are increasingly common, amplifying real-world likelihood. Organizations should prioritize patching within 30 days.

Risk score, explained

CVSS 8.8 reflects: network-accessible vector (AV:N), low attack complexity (AC:L), low privilege required (PR:L), no user interaction needed (UI:N), and high impact across confidentiality, integrity, and availability (C:H/I:H/A:H). The score appropriately captures the severity of unrestricted tool access in a multi-user system. The lack of KEV inclusion indicates no evidence of active in-the-wild exploitation at publication, but the straightforward nature of the bypass and growing LLM security scrutiny warrant assumption of active development of exploits.

Frequently asked questions