AI Agent Security: Practical Controls for Prompt Injection and Beyond

AI agents that can browse the web, call APIs, and execute code represent a step change in capability — and in attack surface. Prompt injection, where untrusted input manipulates an AI agent's behavior, is the most discussed risk, but it's not the only one.

Layers of Defense

No single technique eliminates prompt injection. Effective defenses are layered: input sanitization, instruction isolation (separating system prompts from user data), output validation, and least-privilege tool access. Each layer reduces the probability and blast radius of an attack.

Least Privilege for Agents

An AI agent that can read your database, call external APIs, and send emails has an enormous blast radius. Apply the same least-privilege principles you'd apply to any service: scope tool access to exactly what's needed, require confirmation for destructive actions, and log everything.

Monitor and Audit

Agent behavior should be observable. Log prompts, tool calls, and outputs. Build dashboards that flag anomalies — unexpected tool use, unusual output patterns, or prompt structures that look like injection attempts. Detection is as important as prevention.