The Bluetooth BR/EDR specification up to and including version 5.1 permits sufficiently low encryption key length and does not prevent an attacker from influencing the key length negotiation. This allows practical brute-force attacks (aka "KNOB") that can decrypt traffic and inject arbitrary ciphertext without the victim noticing.
4.4.0-159.1874.4.0-1090.1014.15.0-1047.49~16.04.14.15.0-1041.434.15.0-60.67~16.04.14.15.0-1022.25~16.04.14.4.0-1118.1274.4.0-1122.1284.15.0-60.674.15.0-1047.49Exploitability
AV:AAC:LPR:NUI:NScope
S:UImpact
C:HI:HA:NCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N