Guangquan Xu

The rise of AI agent frameworks has introduced agent skills, modular packages containing instructions and executable code that dynamically extend agent capabilities. While this architecture enables powerful customization, skills execute with implicit trust and minimal vetting, creating a significant yet uncharacterized attack surface. We conduct the first large-scale empirical security analysis of this emerging ecosystem, collecting 42,447 skills from two major marketplaces and systematically analyzing 31,132 using SkillScan, a multi-stage detection framework integrating static analysis with LLM-based semantic classification. Our findings reveal pervasive security risks: 26.1% of skills contain at least one vulnerability, spanning 14 distinct patterns across four categories: prompt injection, data exfiltration, privilege escalation, and supply chain risks. Data exfiltration (13.3%) and privilege escalation (11.8%) are most prevalent, while 5.2% of skills exhibit high-severity patterns strongly suggesting malicious intent. We find that skills bundling executable scripts are 2.12x more likely to contain vulnerabilities than instruction-only skills (OR=2.12, p<0.001). Our contributions include: (1) a grounded vulnerability taxonomy derived from 8,126 vulnerable skills, (2) a validated detection methodology achieving 86.7% precision and 82.5% recall, and (3) an open dataset and detection toolkit to support future research. These results demonstrate an urgent need for capability-based permission systems and mandatory security vetting before this attack vector is further exploited.

Multimodal large language models (MLLMs) have demonstrated significant utility across diverse real-world applications. But MLLMs remain vulnerable to jailbreaks, where adversarial inputs can collapse their safety constraints and trigger unethical responses. In this work, we investigate jailbreaks in the text-vision multimodal setting and pioneer the observation that visual alignment imposes uneven safety constraints across modalities in MLLMs, thereby giving rise to multimodal safety asymmetry. We then develop PolyJailbreak, a black-box jailbreak method grounded in reinforcement learning. Initially, we probe the model's attention dynamics and latent representation space, assessing how visual inputs reshape cross-modal information flow and diminish the model's ability to separate harmful from benign inputs, thereby exposing exploitable vulnerabilities. On this basis, we systematize them into generalizable and reusable operational rules that constitute a structured library of Atomic Strategy Primitives, which translate harmful intents into jailbreak inputs through step-wise transformations. Guided by the primitives, PolyJailbreak employs a multi-agent optimization process that automatically adapts inputs against the target models. We conduct comprehensive evaluations on a variety of open-source and closed-source MLLMs, demonstrating that PolyJailbreak outperforms state-of-the-art baselines.