Disable Open Ports

# Check if port is open and listening
netstat -an | grep -w LISTEN

# On Ubuntu check what ports are used by what services
cat /etc/services | grep -w 53
# domain 53/tcp       # Domain Name Server
# domain 53/udp

# OR
netstat -natp | grep 9090

# Look at documentation for what software needs what ports open

References

Download the CIS benchmark PDF’s from the below link:
https://www.cisecurity.org/cis-benchmarks/

Go to the Operating Systems section and search for the Distribution Independent Linux. Expand it to see more options then download CIS Benchmark.

Other:

• https://access.redhat.com/security/cve/cve-2019-3874
• https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/install-kubeadm/#check-required-ports