The OpenSSH client is supports an undocumented/unknown feature called roaming:

If connection to SSH server breaks/stucked unexpectedly,
and if server supports roaming, then client is able to reconnect to the server and resume the suspended SSH session.

Roaming feature on OpenSSH clients contain a security flaw which allows a malicious SSH server to steal the client’s private keys.

To disable Roaming feature, refer following simple steps and secure your server.

To fix

Add the option ‘UseRoaming no’ in /etc/ssh/ssh_config file and restart ssh service with -oUseRoaming=no included on the ssh command line.

ie, echo ‘UseRoaming no’ >> /etc/ssh/ssh_config

or

sudo sh -c ‘echo UseRoaming \”no\” >> /etc/ssh/ssh_config’

It’s being reported that it effects only on Centos 7 servers and they can update OpenSSH using yum.

#yum update openssh

For more information read official Bug at Redhat Bugzilla