Bluetooth Classic in Bluetooth Core Specification through 5.3 does not properly conceal device information for Bluetooth transceivers in Non-Discoverable mode. By conducting an efficient over-the-air attack, an attacker can fully extract the permanent, unique Bluetooth MAC identifier, along with device capabilities and identifiers, some of which may contain identifying information about the device owner. This additionally allows the attacker to establish a connection to the target device.

An information leakage vulnerability in the Bluetooth Low Energy advertisement scan response in Bluetooth Core Specifications 4.0 through 5.2, and extended scan response in Bluetooth Core Specifications 5.0 through 5.2, may be used to identify devices using Resolvable Private Addressing (RPA) by their response or non-response to specific scan requests from remote addresses. RPAs that have been associated with a specific remote device may also be used to identify a peer in the same manner by using its reaction to an active scan request. This has also been called an allowlist-based side channel.

Bluetooth BR/EDR devices with Secure Simple Pairing and Secure Connections pairing in Bluetooth Core Specification 4.2 through 5.4 allow certain man-in-the-middle attacks that force a short key length, and might lead to discovery of the encryption key and live injection, aka BLUFFS.

Refer: https://www.bluetooth.com/learn-about-bluetooth/key-attributes/bluetooth-security/bluffs-vulnerability/