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Comment by guappa | Hacker News Reader

Docker containers ran as root by default for a great number of years. I'm not even sure if it has now finally been changed.

They provided no sandboxing whatsoever.

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That’s a horrendously bad take, running as uid0 in the container doesn’t mean “no sandboxing whatsoever”. You’re still namespaced with respect to pids/network interfaces/filesystem/etc, and it’s not supposed to be possible to escape it, even when running as root in the container.

Is it possible to do container escapes on occasion? Yes, but each of those is a bug in the Linux kernel that is assigned a CVE and fixed.

Running as non-root in the container is an additional layer of security but it’s not all-or-nothing: doing so doesn’t make you perfectly secure (privilege escalation bugs will continue to exist) and not doing so doesn’t constitute “nothing whatsoever”.

I see you're not aware of `mknod`?

> Is it possible to do container escapes on occasion? Yes, but each of those is a bug in the Linux kernel that is assigned a CVE and fixed.

No bug, if you have permissions to run mknod it's an entirely by design escape that docker lets you do :)

I wasn't talking about kernel bugs, of course there have been a lot of those causing escapes. I am talking about the default configuration that does absolutely 0 sandboxing. And it's not a bug, it's as intended.

If you want to run as root and don't even touch capabilities… yeah it's root. 0 protection, the stuff in the container is running as root and can easily escape namespaces.

I really wonder how can use escape a container given a root shell created by `docker run --rm -it alpine:3 sh` without using a 0day? Using latest Docker and a reasonably up-to-date Linux kernel of course.

With the command above it is still possible to attack network targets, but let's just ignore it here. I just wonder how is it possible to obtain code execution outside the namespace without using kernel bugs.

Can you show me how? Like, if I'm in a stock debian-slim container, and have mknod, and I've started as root, how can I get from inside the container to the host? Could I create files/run program on the host? Portscan localhost? Do something crazy with the docker socket?

> I see you're not aware of `mknod`?

Try harder, friend, those require granted capabilities

  $ PAGER=cat man 7 capabilities | grep -C1 MKNOD

       CAP_MKNOD (since Linux 2.4)
              Create special files using mknod(2).

  $ docker run --rm -it public.ecr.aws/docker/library/ubuntu:24.04 /usr/bin/mknod fred b 252 4
  /usr/bin/mknod: fred: Operation not permitted

It'd be interesting to know what's in your /etc docker configuration :)

Yeah you’re going to need to elaborate and post your sources here. If there’s zero protection at all, show how I can run `docker run -it alpine sh` and break out of the container. Without exploiting any 0days.

No, --privileged doesn’t count. No, --cap-add=<anything> doesn’t count. The claim here is that docker has “zero sandboxing” by default, so you’re going to need to show that you don’t need either of those. Not just moving the goalposts and saying you can break out if you use the command line flag that literally says “privileged”.

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