Your understanding is fine. In many environments, you can still do a lot of damage just by popping a shell and being able to access the database/sensitive environment variables/sensitive code. Getting to root would just be the icing on the cake.

That being said, it's pretty common for non-containerized processes to drop permissions to a low-privileged service account (like nginx running as `nobody`), so it definitely thwarts defense-in-depth in those setups.

In containerized environments, my understanding is their use of namespaces means you still need something more clever than just "patch out the authentication logic in su via the page cache" to escalate permissions in the system to break out of the container. That doesn't mean it's impossible in these exploits (the original copyfail writeup alluded to a second writeup coming to this effect - distinct from dirtyfrag though), but it does mean you're not going to be able to just spam the PoCs floating around.

Also, meant to share some interesting readings. In the Kubernetes world, my RSS feed lit up with their blog post about user namespaces being generally available in k8s 1.36.

They actually provided some example CVEs that wouldn't have been possible if in addition to containers, they were also using user namespaces https://github.com/kubernetes/enhancements/tree/217d790720c5.... The first example talks about "CVE-2019-5736: Host runc binary can be overwritten from container. Completely mitigated with userns." So it seems like getting root in a regular container gives you more of an attack surface, but if user namespaces are deployed, then it's even harder to do anything useful with it. I am looking forward to the aforementioned writeups since user namespace escapes usually mean another kernel bug.