Information
The MaxStartups parameter specifies the maximum number of concurrent unauthenticated connections to the SSH daemon.
To protect a system from denial of service due to a large number of pending authentication connection attempts, use the rate limiting function of MaxStartups to protect availability of sshd logins and prevent overwhelming the daemon.
Solution
Edit or create a file ending in *.conf in the /etc/ssh/sshd_config.d/ directory or the /etc/ssh/sshd_config file and set the MaxStartups parameter as follows:
MaxStartups 10:30:60
Run the following command to comment out any MaxStartups parameter entries in files ending in *.conf in the /etc/ssh/sshd_config.d/ directory or the /etc/ssh/sshd_config file that include any setting greater than 10:30:60 :
# grep -Pi '^s*maxstartupss+(((1[1-9]|[1-9][0-9][0-9]+):([0-9]+):([0-9]+))|(([0-9]+):(3[1-9]|[4-9][0-9]|[1-9][0-9][0-9]+):([0-9]+))|(([0-9]+):([0-9]+):(6[1-9]|[7-9][0-9]|[1-9][0-9][0-9]+)))' /etc/ssh/sshd_config /etc/ssh/sshd_config.d/*.conf | while read -r l_out; do sed -ri "/^s*MaxStartupss+(((1[1-9]|[1-9][0-9][0-9]+):([0-9]+):([0-9]+))|(([0-9]+):(3[1-9]|[4-9][0-9]|[1-9][0-9][0-9]+):([0-9]+))|(([0-9]+):([0-9]+):(6[1-9]|[7-9][0-9]|[1-9][0-9][0-9]+)))/s/^/# /" "$(awk -F: '{print $1}' <<< $l_out)";done