Namespaces are not a security feature, they are... namespaces. In k8s as an example, if you share your PID namespace in a pod, which is a simple config option,

Namespaces are not a security feature, they are... namespaces. In k8s as an example, if you share your PID namespace in a pod, which is a simple config option, you can arbitrarily enter other pod member FS tree with /proc/PID/root, only protected by Unix permissions. Without seacomp, capabilities, SELinux etc... anyone who can launch a docker container can use the --privlaged flag and change host firmware or view any filesystem including the hosts root. Focusing on namespace breakout only misses most of the attack surface.