LPS-Bench: Benchmarking Safety Awareness of Computer-Use Agents in Long-Horizon Planning under Benign and Adversarial Scenarios

Computer-use agents (CUAs) execute multi-stage tasks through tools, where an early unsafe decision can propagate to consequential actions. Evaluating only final outcomes can miss such decisions, while constructing executable environments for new tasks can make benchmark expansion costly. We present LPS-Bench, a benchmark of long-horizon planning safety in MCP-style tool workflows under benign requests and adversarial steering. A template-guided multi-agent pipeline generates user instructions, simulated toolkits, and case-specific safety criteria, followed by human review. This design supports scalable case expansion without building a separate application environment for every test case. LPS-Bench comprises 570 cases derived from 65 scenarios across 7 task domains and 9 planning-risk types, with representative cases additionally adapted to reusable skills. An LLM-based evaluator applies case-specific criteria to complete interaction records, examining tool choices, arguments, and responses to environmental feedback throughout execution. Evaluations of 13 LLM agents reveal persistent failures in both benign and adversarial settings. Prompt-based interventions yield model-dependent gains, but substantial safety failures remain.