auditing-mcp-servers-for-tool-poisoning

# 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 ATLAS **AML.T0010 ML Supply Chain Compromise**). Beyond poisoning, MCP servers introduce classic infrastructure risks: **tool shadowing** (a malicious server overrides a trusted tool's behavior), **rug pulls** (a tool's description changes after the user approved it), **toxic flows** (a combination o...