When using WPA2, EAPOL-Key frames with the Encrypted flag and without the MIC
flag set, the data field was decrypted first without verifying the MIC.  When
the dta field was encrypted using RC4, for example, when negotiating TKIP as
a pairwise cipher, the unauthenticated but decrypted data was subsequently
processed.  This opened wpa_supplicant(8) to abuse by decryption and recovery
of sensitive information contained in EAPOL-Key messages.

See https://w1.fi/security/2018-1/unauthenticated-eapol-key-decryption.txt
for a detailed description of the bug.

Obtained from: FreeBSD