This idea that people have about containers being 'the "OS (really userspace)' is fundamentally wrong. It's the equivalent of a VM, just (hopefully) stripped down to the bare essentials. There's no magic that protects it. The Docker host sure doesn't protect it, and in fact the Docker host can be vulnerable to exploitation from its containers, just as a vSphere host (or any other hypervisor) can be exploited if its VMs are insecure.
This can't happen. There is no "OS" actually running. It's a bunch of binaries and files sitting in a tar archive that the process running can access and link against. What are you going to breach? All the networking, firewalls, kernel, remote access like SSH, and privilege management is the hosts. The only process running in the container is the application.
What you mean is "what if the application running in the container is compromised?" For example what if there's a RCE vuln in the version of libcurl that the app links against? Absolutely! Now you've got a huge problem but this is exactly the same as if there was an RCE in leftPad. In container world that's now the developer's problem instead of yours. Everything in the container is vendored, just pretend it was all statically linked. It's not like an VM where ops patches it.
> It's the equivalent of a VM, just (hopefully) stripped down to the bare essentials
No, no 1000 times no. It's in all ways the equivalent of a process (or tree of processes) running on the host machine. From a security perspective a container is no different than any other binary running on the host. You have it exactly right, there is exactly zero magic and no inherent security.
You should lose exactly as much sleep over outdated container images as you lose over outdated rubygems in your developers' Bundle.lock. Whether that means a lot or a little depends on the company and how security critical the application is.
Would it blow your mind to hear that some devops people actually run more than one application in a container? And that one of those apps might just be sshd? That's one of the many that I know about. Why they wouldn't just run docker exec?
I'm just so sick of the container security shills; in particular I'm tired of people selling debian advisories with zero value add on enterprise contract.
What people hear is "Oh my god you're still running Ubuntu 14.04?!?" but what is actually happening is all the defenses and security boundaries are being enforced by a fully patched RHEL 7 instance with SELinux, the completely unprivileged application code just happens to have an old version of libz bundled with it. So for sure the application is in a position to be compromised depending on how old the libs and the vulns that might exist but that's the developer's concern exactly like their NPM deps.