用权限控制保护AI代理，防攻击且不降低效率

AI agents interact with external environments through tool calls, exposing them to attacks like indirect prompt injection that can trigger unauthorized actions. Securing these agents is challenging: they behave autonomously and probabilistically, security requirements evolve depending on the user's task and execution state, and there is an inherent tradeofff between security and utility. In this work, we introduce Progent, a novel framework that secures AI agents via privilege control. Progent represents privilege as a security policy consisting of symbolic rules over tool names and arguments. These rules specify which tool calls are allowed for task completion and which unnecessary ones are blocked for security. Every tool call is checked against such a policy through a deterministic procedure, enforcing the principle of least privilege. To handle diverse user tasks and evolving execution contexts, an LLM automatically generates the initial policy from the user's task and updates it during execution as new information arrives. Each proposed update is determined by an SMT solver to be either a narrowing (applied automatically) or an expansion (requiring explicit approval), ensuring that the agent's effective action space can only shrink without approval (monotonic confinement). This deterministic update mechanism preserves utility and prevents silent privilege escalation, even when adversarial inputs are present. Our evaluation on popular benchmarks (i.e., AgentDojo and ASB) shows that Progent significantly reduces attack success rates while maintaining high utility. We further validate Progent's practicality by showcasing its effectiveness in real-world agent frameworks such as LangChain and OpenAI Agents SDK.