It was found that the host private key material could possibly leak to the privilege-separated child processes via re-allocated memory. An attacker able to compromise the privilege-separated process could therefore obtain the leaked key information.
It seems that this flaw is not practically exploitable, the leak of host private key material to the privilege-separated child processes is theoretical. No such leak was observed in practice for normal-sized keys, nor does a leak to the child processes directly expose key material to unprivileged users. Because of the this restriction for successful exploitation, this issue has been rated as having Low security impact. A future update may address this flaw.
CentOS6 openssh - Will not fix
CentOS7 openssh - Use openssh-7.4p1-11.el7.x86_64.rpm