hostapd before 2.10 and wpa_supplicant before 2.10 allow an incorrect indication of disconnection in certain situations because source address validation is mishandled. This is a denial of service that should have been prevented by PMF (aka management frame protection). The attacker must send a crafted 802.11 frame from a location that is within the 802.11 communications range.
https://www.openwall.com/lists/oss-security/2019/09/11/7
https://www.debian.org/security/2019/dsa-4538
https://w1.fi/security/2019-7/ap-mode-pmf-disconnection-protection-bypass.txt
https://w1.fi/security/2019-7/
https://usn.ubuntu.com/4136-2/
https://usn.ubuntu.com/4136-1/
https://seclists.org/bugtraq/2019/Sep/56
https://lists.debian.org/debian-lts-announce/2019/09/msg00017.html