Auditing MCP Servers for Tool Poisoning
Authorized-use-only notice: Auditing MCP servers can connect to and probe live tool endpoints. Only scan servers you own or are authorized to assess. Treat scanned tool descriptions as untrusted input — do not load an unaudited MCP server into a privileged agent. Probing third-party MCP endpoints for SSRF or auth weaknesses without permission may be illegal.
Overview
The Model Context Protocol (MCP) lets AI agents discover and call external tools advertised by MCP servers. Each tool exposes a name and a natural-language description that the agent's LLM reads before deciding to call it. In early 2025, Invariant Labs disclosed that this description field is an attack surface: a malicious server can embed hidden instructions in a tool's description (a tool poisoning attack, OWASP MCP03:2025), and a capable model will silently follow them — exfiltrating files, leaking secrets, or redirecting tool calls — while returning a normal-looking response to the user. Because tool descriptions are loaded into the agent's context, tool poisoning is effectively indirect prompt injection delivered through the supply chain (MITRE AT…
