Kubernetes is an open-source container orchestration system for automating software deployment, scaling, and management.

The Shadowserver Foundation started scanning for accessible Kubernetes API instances that respond with a 200 OK HTTP response to the probes.

“We find over 380 000 Kubernetes API daily that allows for some form of access, out of over 450 000 that we are able to identify. Data on these is shared daily in our Accessible Kubernetes API Server Report.”, reads the post published by Shadowserver Foundation.

The result of the scan does not mean these servers are fully open or vulnerable to attacks, it suggests a situation where the servers have an “unnecessarily exposed attack surface”.

They scan all of the IPv4 space on ports 6443 and 443 and include only Kubernetes servers that respond with a 200 OK (with accompanying JSON response), and hence disclose version information in their response.

The post says, “A scan result for 2022-05-16 uncovers 381,645 unique IPs responding with a 200 OK HTTP response to our probes”.

“This is out of the 454,729 Kubernetes API instances we see. The “open” API instances thus constitute nearly 84% of all instances that we can scan for on the Ipv4 Internet.”

Erfan Shadabi, the cyber-security expert with data-security firm Comforte AG, stated that he was unsurprised that the Shadowserver scan discovered so many Kubernetes servers exposed to the public internet.

“White Kubernetes] provides massive benefits to enterprises for agile app delivery, there are a few characteristics that make it an ideal attack target for exploitation”.

“For instance, as a result of having many containers, Kubernetes has a large attack surface that could be exploited if not pre-emptively secured”, he stated.

Protecting Kubernetes

Shadowserver advises that if administrators find that a Kubernetes instance in their environment is accessible to the internet, they should consider implementing ‘authorisation for access,’ or block at the firewall level to reduce the attack surface exposed.

Also, if your Kubernetes API endpoint is available on an IP you were not expecting, and you use kube-proxy in IPVS mode see https[:]//github.com/kubernetes/kubernetes/pull/108460.

Erfan Shadabi suggests that organizations that use containers and Kubernetes in their production environment are to take securing Kubernetes as seriously as they do all aspects of their IT infrastructure.

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