Billions of Bluetooth gadgets bothered by ‘BLURtooth’ miscreant-in-the-middle bug

BORKlife! Flaw allows overwriting of keys by the habitual voyeur

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The Bluetooth Special Interest Group has admitted some previous iterations of its technology had a flaw that could be exploited to hijack or eavesdrop on nearby connections.

Named BLURtooth, aka CVE-2020-15802, the flaw was present in the Bluetooth BR/EDR (Bluetooth Basic Rate/Enhanced Data Rate) from specification version 4.2 to 5.0. The latest version of the Bluetooth spec is 5.2.

Version 4.2 debuted in December 2014 and version 5.0 came along two years later. In 2015 alone the world was cranking out smartphones at a rate of 1.4 billion a year. Just how many other Bluetooth-equipped devices use the flawed specifications is unknowable, though almost certainly in the billions.

And mind-boggling because as Carnegie Mellon University’s CERT explains, they’re “vulnerable to key overwrite, which enables an attacker to gain additional access to profiles or services that are not restricted by reducing the encryption key strength or overwriting an authenticated key with an unauthenticated key.”

As a result, “an attacker could gain additional access to profiles or services that are not otherwise restricted.” Bluetooth carries over the airwaves keyboard presses, audio calls, speaker and headphone audio, etc, etc, so the potential for mischief is significant.

The Bluetooth SIG’s recommendation is that potentially vulnerable implementations “introduce the restrictions on Cross-Transport Key Derivation mandated in Bluetooth Core Specification versions 5.1 and later.”

The organisation is therefore “broadly communicating details on this vulnerability and its remedies to our member companies and is encouraging them to rapidly integrate any necessary patches.” The SIG has also advised Bluetooth users to “ensure they have installed the latest recommended updates from device and operating system manufacturers.”

Which is where this gets tricky because the Bluetooth SIG has more than 20,000 members.

Thankfully the flaw isn’t easy to exploit. As the CERT explains: “Vulnerable devices must permit a pairing or bonding to proceed transparently with no authentication, or a weak key strength, on at least one of the BR/EDR or LE transports in order to be susceptible to attack.

“For example, it may be possible to pair with certain devices using JustWorks pairing over BR/EDR or LE and overwriting an existing LTK or LK on the other transport. When this results in the reduction of encryption key strength or the overwrite of an authenticated key with an unauthenticated key, an attacker could gain additional access to profiles or services that are not otherwise restricted."

École Polytechnique Fédérale de Lausanne and Purdue University were credited with independently verifying the flaw. ®

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