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Bluetooth transfers from all devices are under severe threat due to a series of vulnerabilities in the Bluetooth standard. These vulnerabilities are collectively called as BLUFFS and can compromise the secrecy of Bluetooth sessions.
The attacks can enable device impersonation and man-in-the-middle (MitM) attacks. The latest Bluetooth vulnerabilities were discovered by Daniele Antonioli at Eurecom, and exploit two previously unknown flaws in the Bluetooth Core Specification (versions 4.2 through 5.4), compromising the forward and future secrecy of Bluetooth sessions.
The vulnerabilities, tracked under the identifier CVE-2023-24023, operate at an architectural level, affecting a wide range of devices, including laptops, smartphones, and various other mobile devices. This makes billions of devices vulnerable to BLUFFS attacks, reports BleepingComputer.
To execute BLUFFS, an attacker needs to be within Bluetooth range of the targeted device. The attacker then impersonates one device to negotiate a weak session key with the other device. The attacks do not require user interaction or compromise Bluetooth pairing keys.
The BLUFFS toolkit, shared on GitHub by the researchers, includes a Python script for testing the attacks, ARM patches, parsers, and PCAP samples captured during their experiments.
BLUFFS impacts Bluetooth versions ranging from 4.2, released in December 2014, to the latest 5.4 version, launched in February 2023.
In response to these findings, Eurecom researchers propose backwards-compatible modifications to enhance session key derivation and mitigate BLUFFS. Suggestions include introducing a new Key Derivation Function (KDF) for Legacy Secure Connections, shared pairing keys for mutual authentication, enforcing Secure Connections mode, and maintaining a cache of session key diversified.
Bluetooth SIG, the organisation overseeing Bluetooth standard development, has acknowledged Eurecom’s report and published recommendations on its website. These recommendations advise implementations to reject connections with low key strengths, use higher encryption strength levels, and operate in ‘Secure Connection Only’ mode during pairing.
“Implementations are advised to reject service-level connections on an encrypted baseband link with key strengths below 7 octets. For implementations capable of always using Security Mode 4 Level 4, implementations should reject service-level connections on an encrypted baseband link with a key strength below 16 octets. Having both devices operating in Secure Connections Only Mode will also ensure sufficient key strength,” Bluetooth SIG said in an advisory.
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