Lab Guide Shows How Browser Agents Fall for Hidden Prompt Injection Attacks
A technical lab exercise published on DEV Community demonstrates how browser-based AI agents can be manipulated through indirect prompt injection, where hostile instructions are embedded in web page content. The attack exploits a confused-deputy pattern, causing the agent to execute unintended actions — such as sending a POST request — simply by reading a page the user asked it to summarize. The lab walks participants through building a local attacking page, an action-recording sink, and an audit log to capture agent behavior under both vulnerable and hardened configurations. Researchers can then compare outcomes between a permissive policy profile and a hardened one that treats page content as untrusted, restricts destinations, and requires user approval for consequential actions. The exercise is model-agnostic, runs entirely on local services using dummy data, and is designed to highlight the critical trust boundary between web content and an agent's operational authority.
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