MCP Tool Poisoning Prevention: Gateway Controls for the Model Context Protocol Surface
Model Context Protocol tool poisoning is the agentic analog to supply-chain compromise. An MCP server presents a set of tools to an agent host; an attacker who controls the MCP server (or the tool definitions an MCP server advertises) can change what the tools do, what they return, or what parameters they accept. The agent loop calls the tool in good faith and the actions executed against downstream systems are the attacker'"'"'s. The prevention surface splits across MCP server selection, tool-definition pinning, and per-decision authorization at the agent-tool boundary. This article walks through the MCP poisoning patterns and the gateway controls that contain them.