A container filesystem is the isolated file space a container sees at runtime. It usually includes a minimal read-only image plus a writable layer, and it is separated from the host operating system. Processes inside the container read and write files as if they were on a normal machine, but their view is confined to that container’s namespace and storage layers.
This isolation matters because many attacks try to cross the boundary between container and host. A secure container filesystem helps reduce the impact of malware, limit access to sensitive host data, and keep application files contained. Defenders still need to watch for volume mounts, weak permissions, and bugs in file-handling tools: if a copy, extract, or path-resolution flaw lets data escape the intended destination, files may land outside the container or overwrite host paths. In practice, container filesystems are a key trust boundary in both exploitation and defense.