Are nested namespaces a security concern?

The Water Cooler
1

I’m not proficient in how the Linux kernel works. I’ve observed that nested namespaces are not allowed in Flatpak. Are we unable to trust the kernel for nested namespace usage due to the attack surface? As far as I know, there’s no issue with nested seccomp and nested landlock. However, nested namespaces are seen as a security concern, and I can’t understand why due to my ignorance. I would appreciate it if you could enlighten me.