A new vulnerability, CVE-2018-1111, has been recently announced; it allows a malicious DHCP server to send a specially crafted response that can run privileged commands on a DHCP client that is running dhclient. This affects dhclient on both Centos Linux 6 and CentOS Linux 7 systems.
RedHat have released an updated to patch the flaw in dhclient. It can be assumed that versions of before dhclient-4.2.5-68.el7 are vulnerable.
yum update dhclient
For more information about the vulnerability, see RedHat’s post here: https://access.redhat.com/security/vulnerabilities/3442151