Raesene's Ramblings

After talking about the release of PCIs recommendations for containers and container orchestration environments, and how it could be applied to Kubernetes clusters in my last blog I thought that it might be a good idea to discuss some of the general challenges that assessors and auditors might have when looking at Kubernetes environments, as there’s quite a few variables that you need to account for. This is part of a longer series on the PCI guidance for containers, and an index of the posts in this series can be found here.

Yesterday, the PCI Council issued a new information supplement that should be of specific interest to anyone using container technologies like Docker and podman and Container orchestration technologies like Kubernetes and OpenShift to process cardholder transactions.

Windows containers don’t get quite the use of their Linux brethren, but they’re an interesting topic and one that’s seeing more adopting as enterprises move to Containerization. Whilst, from a Docker/Kubernetes perspective, they look relatively similar to Linux containers, the underlying isolation mechanisms are entirely different. A new development in this is the provision of “host process” containers, so I thought it would be fun to take a look at what’s possible with them, but first some background…

I was doing some reading on the topic of Kubernetes RBAC this week and I realised that a good article on the topic of auditing RBAC by Mark Manning had unfortunately succumbed to bitrot (Although the wayback machine still has a copy), so I thought it would be a good opportunity to revisit the topic as there are some interesting nuances to it.

Capabilities are an interesting area of Linux security and one which has some application to containers. Whilst the details of how they work have been well documented (I’d recommend reading Adrian Mouat’s two part series here and here) I thought it was worth looking at a couple of neat tricks we can use do with file capabilities when using containers.

There’s been a couple of studies recently released by security research companies about exposed Kubernetes clusters on the Internet, and whilst it’s nice to see the security industry focusing a bit more on Kubernetes, some of the analysis misses some of the details of why Kubernetes clusters are exposed to the Internet and what some of the results mean, so I thought it would be a good opportunity to revist this topic, also as there have been some developments in what information can be found via Internet search engines.

There are lots of tools which we can use in the container ecosystem to easily create and test applications, but sometimes the networking they create can get a little complex, making it hard to work with and troubleshoot. I came across a scenario recently (for a workshop in Kubecon) where I needed to access a GUI application deployed in a KinD cluster running in an EC2 instance on AWS, from my laptop. The solution I came up with was to use Tailscale and as it seemed like a nice way to solve the problem, I thought it was worth documenting.

Before I get into this post a quick note that there is no dramatic payoff here, it’s just playing around with something that surprised me in Kubernetes, to understand a bit about what’s going on.

This week there was some research published from Cambridge university called “Trojan Codes”, around the potential risks of RTL unicode characters in source code. Whilst this is very much not a new problem, there have been various pieces of research over the years about the difficulties of handling unicode characters, it seemed like a good cue to look at this kind of issue in the context of Kubernetes. So far I’ve not found any security issues caused by this, but I found a couple of things which could be of interest, so thought I’d write it down, in case it’s useful to anyone.

I was playing around with CRDs today when I wondered “what would happen if I tried to overwrite one of Kubernetes’ core object types? The results weren’t what I expected, so thought it was worth writing it down, in case it comes as a surprise to others :) N.B. There’s an update at the bottom which sheds more light on what happens when you do this