A vulnerability in the Split DNS feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. The vulnerability occurs because the regular expression (regex) engine that is used with the Split DNS feature of affected releases may time out when it processes the DNS name list configuration. An attacker could exploit this vulnerability by trying to resolve an address or hostname that the affected device handles. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.