An MCP server is a program that implements the Model Context Protocol, exposing specific tools, data, or capabilities that MCP clients—typically AI agents or assistants—can request and use.

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Main takeaways

• The MCP server is the resource-providing side of the MCP architecture: it defines what an AI agent can actually do or access in the real world.
• Each MCP server exposes a defined set of tools (functions an agent can call), resources (data an agent can read), and prompts (templates for common interactions).
• MCP servers represent a new category of access pathway: they connect AI systems to organizational data and systems through channels that may not be visible to existing security monitoring.
• The governance questions around MCP servers are the same as for any privileged integration: what can it access, who authorized it, and is that access still appropriate?

What is an MCP server?

In the Model Context Protocol architecture, a server is a program that sits between an AI agent (the MCP client) and the systems, data, or services the agent needs to interact with. The server implements the MCP protocol, advertises its capabilities to connecting clients, and handles the actual execution when a client requests an action.

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An MCP server might expose the ability to search a codebase, read and write files, query a database, interact with a SaaS API, browse the web, execute code, or retrieve information from internal documentation. From the agent's perspective, it simply sends a request to the server; the server handles whatever integration, authentication, and execution is required to fulfill it.

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The MCP server model is modular by design: different servers can be deployed for different capabilities, and agents can connect to multiple servers depending on what their task requires. This composability is what makes MCP powerful—and what creates the governance challenge.

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Types of MCP servers

MCP servers span a wide range of scope and sensitivity:

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Local servers—Run on the user's own machine, often to provide file system access, code execution, or interaction with locally installed applications. These have access to whatever the user's machine and account can reach.

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Remote servers—Run as network services, providing access to SaaS APIs, databases, internal tools, or other shared resources. These can be accessed by any authorized MCP client, potentially including agents running on behalf of multiple users.

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Third-party servers—Built by vendors or the open-source community to provide integration with specific services (GitHub, Slack, Google Drive, Salesforce). These are increasingly available through registries and marketplaces, making them easy to deploy without security review.

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Custom enterprise servers—Built internally to provide agents access to proprietary systems, internal APIs, or sensitive data stores.

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The security dimension

MCP servers are, at their core, access management artifacts. They define what an AI agent can reach. That makes them subject to the same governance principles that apply to any other access pathway.

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Key security considerations:

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Authentication and authorization. How does the MCP server verify that a connecting client is authorized? What scopes or permissions does it enforce? A server with no authentication or overly permissive authorization becomes a broad access grant for any agent that can connect to it.

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Data access scope. What organizational data can the server reach? A file system server, a database connector, or a SaaS API server may have access to highly sensitive data. The server's deployment and configuration determine the blast radius if that access is abused.

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Inventory and discovery. MCP servers deployed by developers or power users may not be visible to security teams. As with shadow SaaS, servers created informally represent ungoverned access pathways.

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Third-party server risk. Community or vendor-provided MCP servers introduce third-party risk similar to any third-party integration: what does the server's code actually do, what data does it have access to, and who maintains it?

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Action scope. Some MCP servers are read-only; others can write, delete, or trigger actions in connected systems. The appropriate governance level depends on what actions the server exposes.

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See how Nudge Security discovers and governs AI integrations and agentic access pathways →