Small language models (SLMs) have emerged as promising alternatives to large language models (LLMs) due to their low computational demands, enhanced privacy guarantees, and comparable performance in specific domains. Deploying SLMs on edge devices, such as smartphones and smart vehicles, has become a growing trend. However, the security implications of SLMs have not received as much attention as those of LLMs, particularly concerning the significant jailbreak threats they face. In this paper, we conduct the first systematic empirical study of SLMs' vulnerabilities to jailbreak attacks. Through systematic evaluation on 59 SLMs from 15 mainstream SLM families against 12 state-of-the-art jailbreak methods, we demonstrate that 61.0% of evaluated SLMs show an average ASR of more than 40% under jailbreak attacks and 37.3% of them have an ASR of more than 50% on direct harmful queries. Through correlation analysis, we identify that SLM vulnerabilities are closely related to training details (e.g., training dataset and method) rather than model size scaling. We further evaluate five defenses for jailbreak attacks, revealing that prompt-level defenses remain inconsistent across SLMs and attack methods, while model-level defense improves robustness against similar attacks yet generalizes poorly to multi-turn attacks such as Crescendo, highlighting the urgent need for security-by-design approaches in SLM development.

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