A vulnerability in Cisco IOS XE Wireless Controller Software for Cisco Catalyst 9800 Series Routers could allow an unauthenticated, adjacent attacker to send ICMPv6 traffic prior to the client being placed into RUN state. The vulnerability is due to an incomplete access control list (ACL) being applied prior to RUN state. An attacker could exploit this vulnerability by connecting to the associated service set identifier (SSID) and sending ICMPv6 traffic. A successful exploit could allow the attacker to send ICMPv6 traffic prior to RUN state.