Agent-Fence: Mapping Security Vulnerabilities Across Deep Research Agents

Large language models are becoming deep agents that plan, persist state, and invoke tools, shifting safety failures from unsafe text to unsafe trajectories. We introduce AgentFence, an architecture-centric security evaluation that defines 14 trust-boundary attack classes across planning, memory, retrieval, tool use, and delegation, and detects failure via trace-auditable conversation breaks: unauthorized or unsafe tool use, wrong-principal actions, state or objective integrity violations, and attack-linked deviations. Holding the base model fixed, we evaluate eight agent archetypes under persistent multi-turn interaction and find substantial architectural variation in mean security break rate (MSBR), from 0.29 ± 0.04 for LangGraph to 0.51 ± 0.07 for AutoGPT. The highest-risk classes are operational: Denial-of-Wallet at 0.62 ± 0.08, Authorization Confusion at 0.54 ± 0.10, Retrieval Poisoning at 0.47 ± 0.09, and Planning Manipulation at 0.44 ± 0.11, while prompt-centric classes remain below 0.20 under standard settings. Breaks are dominated by boundary violations: SIV 31%, WPA 27%, UTI plus UTA 24%, and ATD 18%. Authorization confusion correlates with objective and tool hijacking, with rho approximately 0.63 and rho approximately 0.58, respectively. AgentFence reframes agent security around what matters operationally: whether an agent stays within its goal and authority envelope over time.