Optimus: association-based dynamic system call filtering for container attack surface reduction

While container adoption has witnessed significant growth in facilitating the operation of large-scale applications, this increased attention has also attracted adversaries who exploit numerous vulnerabilities present in contemporary containers. Unfortunately, existing security solutions largely overlooked the need to restrict container access to the shared host kernel, particularly exhibiting critical limitations in enforcing the least privilege for containers during runtime. Hence, we propose Optimus, an automated and comprehensive system that confines container operations and governs their interactions with the host kernel using an association-based system call filtering. Optimus efficiently identifies the essential system calls required by containers and enhances their security posture by dynamically enforcing the minimal set of system calls for each container during runtime. This is achieved through (1) lightweight system call monitoring leveraging eBPF, (2) system call validation via association analysis, and (3) dynamic system call filtering by adopting covert container renewal. Our evaluation shows that Optimus effectively minimizes the necessary system calls for containers while maintaining their serviceability and operational efficiency during runtime.