Multimodal-SEA: Benchmarking AI Agent Security under Multimodal Social Engineering Attacks

Multimodal large language model (MLLM)-based mobile agents are rapidly evolving from conversational assistants into autonomous systems that perceive, reason over, and act on smartphone environments. This capability also exposes a new security risk: adversaries can embed malicious objectives in cross-application mobile content and steer agent behavior through indirect multimodal injection. Although prompt injection has been studied in desktop and web settings, its cross-modal properties in mobile ecosystems remain poorly understood, and existing security analyses are still limited. To close this gap, we introduce MobileInject, the first benchmark for evaluating mobile agents against multimodal injection attacks and reasoning-to-action security risks. MobileInject provides a high-fidelity interactive mobile evaluation framework covering 11 scenarios, 9 security-risk categories, and 108 executable risk instances. It further introduces Cross-Modal Consistency Injection to exploit corroboration across modalities, two enhanced attack methods, Multi-Role Collaborative Deception and Reasoning-Camouflage Injection, to intensify trust manipulation and reasoning hijacking, and a Reasoning Security Diagnosis Framework for fine-grained failure analysis. Systematic experiments show that mobile agents are broadly vulnerable to multimodal injection, and that many failures stem from reasoning hijacking at early stages. These findings establish MobileInject as a systematic cross-modal benchmark for studying and improving the security of mobile agents. Code release details are provided in the Appendix Open Science section.

Safety evaluation of multimodal large language models requires tracking not only whether an attack succeeds, but also how the interaction unfolds across turns and input modalities. We present MUSE (Multimodal Unified Safety Evaluation), an open-source, browser-based, run-centric platform for multimodal safety evaluation. MUSE treats each attack run as the persistent unit of execution, inspection, and analysis, preserving its configuration, multi-turn trajectory, delivered modalities and media, target responses, and safety judgments. A five-level response taxonomy further distinguishes full Compliance from Partial Compliance and refusal behavior, yielding hard ASR, soft ASR, and gray-zone width (GZW). Across 11,700 evaluations on six multimodal LLMs, direct text-only requests yield only 3.1% macro hard ASR and 4.4% soft ASR, while iterative attack procedures are substantially more effective. Attack effectiveness also varies substantially with the attacker backbone. In contrast, Inter-Turn Modality Switching (ITMS), evaluated as a controlled delivery-modality probe, does not consistently increase attack success. These results demonstrate the value of run-centric, fine-grained evaluation for characterizing multimodal safety behavior beyond a single binary success metric.

An AI agent can prepare an accurate report and still request an action its user has not authorized. Cooperation across Web services therefore requires separate judgments about identity, evidentiary support, and permission. We define synthetic social engineering (SSE) as deliberately deceptive or misleading influence intended to exploit AI recipients' responses to credibility, authority, or obligation cues and redirect behavior away from authorized objectives. We focus on separately tasked sender agents that produce or adapt misleading communication. Drawing on cybersecurity, social engineering, and persuasion research, we develop an operational framework connecting actors, deceptive representations, candidate influence routes, evidence or permission boundaries, responses, and consequences. The framework distinguishes attempts from successful redirection, without assuming human psychological processes. We implement it in the Agent Service Exchange and Evidence Commons (ASE-EC), a reproducible testbed with independently specified records and authorization scopes. Across 1,260 research episodes using Qwen3-4B in two fictional briefing tasks, matched comparisons test authority and commitment appeals, while defense comparisons assess protection alongside authorized task completion. Invoking a limited prior agreement increased unauthorized requests from 43.3% to 96.7%, although recipients retained supported decisions and permissions remained unchanged. These controlled findings identify action selection as a distinct security concern, even when evidence handling succeeds, and they provide a reusable basis for evaluating safeguards that preserve useful cooperation across Web services.