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On CentOS servers, we can enable the automatic download and installation of security updates using the yum-cron package.  To get started install the unattended upgrades package
Install the  yum-cron package.

# Install yum-cron
sudo yum install yum-cron

Edit the yum-cron.conf file

sudo nano /etc/yum/yum-cron.conf

Edit the file with the following

#Install security updates
update_cmd = security
#Install the updates after downloading
apply_updates = yes
#Spread the update start time over an hour 
random_sleep = 60

Startup the service:

# Make sure yum-cron starts at boot-up
sudo systemctl enable yum-cron
# finally start up the service
sudo systemctl start yum-cron

You can check on the status any time by doing:

sudo systemctl status yum-cron

Advanced topics

Choosing which updates to install

#  What kind of update to use:
# default                            = yum upgrade
# security                           = yum --security upgrade
# security-severity:Critical         = yum --sec-severity=Critical upgrade
# minimal                            = yum --bugfix upgrade-minimal
# minimal-security                   = yum --security upgrade-minimal
# minimal-security-severity:Critical =  --sec-severity=Critical upgrade-minimal
update_cmd = default

Getting email updates.

# How to send messages.  Valid options are stdio and email.  If
# emit_via includes stdio, messages will be sent to stdout; this is useful
# to have cron send the messages.  If emit_via includes email, this
# program will send email itself according to the configured options.
# If emit_via is None or left blank, no messages will be sent.
emit_via = email

[email]
# The address to send email messages from.
email_from = centos@myserver

# List of addresses to send messages to.
email_to = test@example.com

# Name of the host to connect to to send email messages.
email_host = localhost