Linux

It is the application Docker that is not secure. Containers are. In fact Docker runs a daemon as root to wich you communicate from a client. This is what makes it less secure; running under root power. It also has a few shortcomings of privileged containers. This can be easily solved by using podman and SELinux. If you can manage to run Docker rootless, then you are magnitudes higher in security.

Try using LXD

Docker has an additional issue, but not one unique to docker. Like flatpak, pip, composer, npm or even back to cpan and probably further, as a third-party source of installed software, it breaks single-source of truth when we want to examine the installed-state of applications on a given host.

I've seen iso27002/12.2.1f, I've seen supply-chain management in action to massive benefit for uptime, changes, validation and rollback, and it's simplified the work immensely.

    .1.3.6.1.2.1.25.6.3

If anyone remembers dependency hell - which is always self-inflicted - then this should be Old Hat.

HAVING SAID THAT, I've seen docker images loaded as the entire, sole running image, apparently over a razor-thin bmc-sized layer, on very small gear, to wondrous effect. But - and this is how VMware did it - a composed bare micro-image with Just Enough OS to load a single container on top, may not violate 27002 in that circumstance.

Where did you read that and which arguments did the authors make?

Many times, the configuration of Docker is the issue, e.g. mounting stuff like files from /etc/ or the Docker socket from the outside, using insecure file permissions or running the application as root user.

If you use rootless Docker or Podman, you already eliminated one of the security risks. The same goes for the other mentioned things.

What exactly do you mean by "questionable programs"? If you want to run malware, you shouldn't do so in an environment where it can break out of anything. There's the possibility of hardware virtualisation which prevents many of the outbreaks possible, but even then, exploits have been found.

You're really only secure if you run questionable software on an airgapped computer with no speakers and never run anything else on it.

What would be your use case?

All recent CPUs have native virtualization support, so there's close to no performance hit on VMs.

That being said, even a VM is subject to exploits and malicious code could break out of the VM down to its hypervisor.

The only secure way of running suspicious programs starts with an air-gaped machine, a cheap hdd/ssd that will go straight under the hammer as soon as testing is complete. And I'd be wondering even after that if maybe the BIOS might have been compromised.

On a lower level of paranoia and/or threat, a VM on an up-to-date hypervisor with a snapshot taken before doing anything questionable should be enough. You'd then only have to fear a zero day exploit of said hypervisor.