It should be apparent that much of WiFi operation relies on trust, particularly with regard to the validity of source and destination addresses. Given these values may be spoofed, it’s with the technique of frame injection that various attacks may be carried out.
Simply put, frame injection is the process of transmitting any WiFi frame desired, regardless of an association with any station. One example may be a beacon frame injected into the air with specific values set to aid the penetration tester.
Another example may be a deauthentication frame with a spoofed source and destination address. Not all radios and software support this ability. This technique is leveraged by the PineAP suite for a number of attacks using the WiFi Pineapple hardware.