A vulnerability in the implementation of Point-to-Point Tunneling Protocol (PPTP) functionality in Cisco Aironet 1810, 1830, and 1850 Series Access Points could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient validation of Generic Routing Encapsulation (GRE) frames that pass through the data plane of an affected access point. An attacker could exploit this vulnerability by initiating a PPTP connection to an affected access point from a device that is registered to the same wireless network as the access point and sending a malicious GRE frame through the data plane of the access point. A successful exploit could allow the attacker to cause the NSS core process on the affected access point to crash, which would cause the access point to reload and result in a DoS condition. This vulnerability affects Cisco Aironet 1810, 1830, and 1850 Series Access Points that are running Cisco Mobility Express Software Release 8.4.100.0, 8.5.103.0, or 8.5.105.0 and are configured as a master, subordinate, or standalone access point. Cisco Bug IDs: CSCvf73890.