ETDI: Mitigating Tool Squatting and Rug Pull Attacks in Model Context Protocol (MCP) by using OAuth-Enhanced Tool Definitions and Policy-Based Access Control (2506.01333v1)

Abstract: The Model Context Protocol (MCP) plays a crucial role in extending the capabilities of LLMs by enabling integration with external tools and data sources. However, the standard MCP specification presents significant security vulnerabilities, notably Tool Poisoning and Rug Pull attacks. This paper introduces the Enhanced Tool Definition Interface (ETDI), a security extension designed to fortify MCP. ETDI incorporates cryptographic identity verification, immutable versioned tool definitions, and explicit permission management, often leveraging OAuth 2.0. We further propose extending MCP with fine-grained, policy-based access control, where tool capabilities are dynamically evaluated against explicit policies using a dedicated policy engine, considering runtime context beyond static OAuth scopes. This layered approach aims to establish a more secure, trustworthy, and controllable ecosystem for AI applications interacting with LLMs and external tools.

• The paper presents a framework that integrates cryptographic identity verification, OAuth, and policy-based access control to secure MCP integrations.
• It employs immutable, versioned tool definitions to prevent tool poisoning and rug pull attacks in MCP systems.
• The study demonstrates enhanced runtime security through dynamic evaluations and fine-grained access control, ensuring verifiable trust and minimal risk exposure.

Overview of Enhanced Tool Definition Interface (ETDI) for Secure Model Context Protocol Integration

The paper introduces a significant security enhancement framework for the Model Context Protocol (MCP) used in the integration of external tools with LLMs. The Enhanced Tool Definition Interface (ETDI) is proposed as a robust security layer aimed at mitigating risks associated with integrating these external systems, specifically addressing vulnerabilities like Tool Poisoning and Rug Pull attacks. The framework utilizes OAuth-enhanced tool definitions alongside policy-based access control to ensure a secure ecosystem for MCP applications.

MCP Architecture and Security Flaws

Initially, the paper outlines the MCP architecture, which operates through a distributed client-server model involving host applications, MCP clients, servers, and resources. The integration aims to augment the capabilities of LLMs, but the openness of the standard MCP facilitates security risks, particularly from Tool Poisoning and Rug Pull attacks. Tool Poisoning involves malicious tools impersonating legitimate ones, whereas Rug Pull attacks occur when legitimate tools change their functionality post-approval to perform unauthorized actions.

ETDI Security Extensions

Cryptographic Identity Verification: ETDI begins with cryptographic verification to confirm the authenticity and integrity of tool definitions. Tool providers generate cryptographic keys, and tool definitions are signed digitally. This ensures that even if a tool description is spoofed, the signature verification can confirm its authenticity, thus preventing Tool Poisoning.

Immutable and Versioned Definitions: The framework introduces an immutable, versioned definition system where any change in tool functionality or metadata requires a new version and re-approval, thwarting Rug Pull attacks. Immutable definitions tied to cryptographic identities ensure operational transparency and user trust.

OAuth Integration: By integrating OAuth 2.0, ETDI standardizes permission management, enabling granular access control through scopes. OAuth authentication bolsters overall security, allowing dynamic evaluations of tool actions against specified permissions via JSON Web Tokens (JWT), without relying solely on static scopes.

Policy-Based Access Control

ETDI further extends security through policy-based access control, where tool actions are dynamically evaluated through policy engines like Open Policy Agent and Amazon Verified Permissions. These systems offer contextual and fine-grained access control beyond the static OAuth scopes, considering runtime attributes such as user context, data sensitivity, location, and time, thus enhancing decision processes related to tool invocations.

Security Analysis and Implications

The combined approach of cryptographic signatures, OAuth scopes, and policy engine evaluations significantly enhances the security posture against MCP vulnerabilities. The layered security model ensures that any authorized tool actions are conducted strictly under verifiable trust and explicit user consent, adapting to runtime requirements. This multi-faceted framework positions MCP applications to securely integrate real-world capabilities, bolstering user confidence and broadening the scope of practical LLM applications.

Future Directions

The paper points towards potential future developments in decentralized identity management using Verifiable Credentials and Decentralized Identifiers to further reduce reliance on centralized authorities. Additionally, incorporating automated behavioral analysis of tools against declared permissions could further complement security measures in MCP ecosystems.

Conclusion

ETDI, along with OAuth and policy-based access control, represents a critical advancement in securing MCP integrations. While the system's complexity might pose implementation challenges, its security benefits make it a compelling solution for future MCP applications needing robust, trustworthy engagement with external systems. By ensuring verifiable trust paths and minimal risk exposure, ETDI demonstrates a forward-thinking approach to AI integrations and security.