"etcd is a distributed key-value store. In fact, etcd is the primary datastore of Kubernetes; storing and replicating all Kubernetes cluster state. As a critical component of a Kubernetes cluster having a reliable automated approach to its configuration and management is imperative."
What this means in english is that etcd stores the current state of the Kubernetes cluster usually including the kubernetes tokens and passwords. If you check out the following references you can get a sense for the pain level that could potentially be involved. At minimum you can get network info or running pods and at best credentials.
the second link talks extensively around types of info the found when they hit all the shodan endpoints for 2379 and did some analysis on the results.
If you manage to find open etcd the easiest way to check for creds is to just do a curl request for:
Example Loot -
Usually it's boring stuff like this:
But occasionally you'll get more interesting things like:
or more fun things like kublet tokens: