Further reading

Trail of Bits and Atredis Partners have done a good job on Kubernetes components' threat modeling. Their whitepaper highlights in detail the threats in each Kubernetes component. You can find the whitepaper at https://github.com/kubernetes/community/blob/master/wg-security-audit/findings/Kubernetes%20Threat%20Model.pdf.

Note that the intent, scope, and approach of threat modeling was different for the preceding whitepaper. So, the results will look a little different.