Mind the Web: The Security of Web Use Agents

Web-use agents are rapidly being deployed to automate complex web tasks, operating with extensive browser capabilities including multi-tab navigation, DOM manipulation, JavaScript execution and authenticated session access. However, these powerful capabilities create a critical and previously unexplored attack surface. This paper demonstrates how attackers can exploit web-use agents' high-privilege capabilities by embedding malicious content in web pages such as comments, reviews, or advertisements that agents encounter during legitimate browsing tasks. In addition, we introduce the task-aligned injection technique that frame malicious commands as helpful task guidance rather than obvious attacks. This technique exploiting fundamental limitations in LLMs' contextual reasoning: agents struggle in maintaining coherent contextual awareness and fail to detect when seemingly helpful web content contains steering attempts that deviate from their original task goal. Through systematic evaluation of four popular agents (OpenAI Operator, Browser Use, Do Browser, OpenOperator), we demonstrate nine payload types that compromise confidentiality, integrity, and availability, including unauthorized camera activation, user impersonation, local file exfiltration, password leakage, and denial of service, with validation across multiple LLMs achieving success rates of 80%-100%. These payloads succeed across agents with built-in safety mechanisms, requiring only the ability to post content on public websites, creating unprecedented risks given the ease of exploitation combined with agents' high-privilege access. To address this attack, we propose comprehensive mitigation strategies including oversight mechanisms, execution constraints, and task-aware reasoning techniques, providing practical directions for secure development and deployment.