According to the CERT Management Center at Carnegie Mellon University, the defect makes Bluetooth devices vulnerable to a variety of possible hacking risks, including Man in the Middle ( MiTM) attacks. Although the problem only arises when certain devices execute pairings without authentication or have insufficient key protection, the flaw will also cause attackers to reduce encryption security by overwriting an authenticated key with an unauthorised key.
Researchers claim that dual-mode Bluetooth systems that support both Bluetooth BR / EDR and LE using Cross-Transport Key Derivation (CTKD) for pairing are at risk from key overwrite vulnerabilities, allowing attackers to gain access to unregulated profiles or services on compromised devices. In order for this attack to be successful, an attack device will need to be within the wireless range of a compromised Bluetooth system following any of the above listed requirements.
The Bluetooth SIG took care of the problem and released a comment about how to minimise the hazard. The organisation advises that “potentially insecure applications impose limitations on the Cross-Transport Key Derivation required in Bluetooth Core Specification versions 5.1 and later.” The association also urged Bluetooth consumers to ensure that they enabled the most recent suggested upgrades from their computer manufacturers.
Several possible attacks may be carried out by leveraging CVE-2020-15802, including a Man in the Middle ( MITM ) attack. The weakness is referred to as BLURtooth and the party of attacks is referred to as BLUR attacks. Vulnerable devices must allow the pairing or bonding of at least one of the BR / EDR or LE transports to continue transparently with no authentication or poor key strength in order to be vulnerable to attack. For example, it may be possible to pair with some devices using JustWorks and pair over BR / EDR or LE and overwrite the current LTK or LK on the other transport. If this results in a reduction of the encryption key strength or overwriting of an authentication key with an unauthorised key, an attacker can obtain additional access to accounts or services that are not otherwise limited.
Bluetooth SIG has published guidelines to alleviate this issue, which include additional compliance checks to ensure that the overwrite of an authenticated key or key of a specified length with an unrecognised key or a reduced length key is not allowed in devices supporting Bluetooth Core Specification version 5.1 or higher. They further propose that potentially insecure applications enforce limitations on the CTKD required in Bluetooth Core Specification version 5.1 and later. Implementations can preclude overwriting of the LTK or LK for one transport with the LTK or LK extracted from the other if overwriting would result in either a reduction in the main strength of the original bonding or a reduction in the MITM security of the original bonding (from authenticated to non-authenticated). This can enable the host to log the agreed key duration and authentication status in the Bluetooth Security Database.
In addition, the Bluetooth SIG advises that devices limit when they are pairable on either transport to times when the user interaction takes the device in pairable mode or when the system has no links or current contacts to the paired device. In all cases, it is advised that devices limit the length of the pairing mode and delete the current bonding only if the devices are specifically in pairing mode.