Hacker Rewarded $70,000 for Finding Way to Bypass Google Pixel Phones’ Lock Screens

Google has resolved a high-severity security issue affecting all
Pixel smartphones that could be trivially exploited to unlock the
devices.

The vulnerability, tracked as CVE-2022-20465
and reported by security researcher David Schütz in June 2022, was
remediated as part of the search giant’s monthly Android update^[1]
for November 2022.

“The issue allowed an attacker with physical access to bypass
the lock screen protections (fingerprint, PIN, etc.) and gain
complete access to the user’s device,” Schütz, who was awarded
$70,000 for the lock screen bypass, said^[2]
in a write-up of the flaw.

The problem, per the researcher, is rooted in the fact that lock
screen protections are completely defeated when following a
specific sequence of steps –

• Supply incorrect fingerprint three times to disable biometric
  authentication on the locked device
• Hot swap^[3]
  the SIM card in the device with an attacker-controlled SIM that has
  a PIN code set up
• Enter incorrect SIM pin thrice when prompted, locking the SIM
  card
• Device prompts user to enter the SIM’s Personal Unlocking Key
  (PUK) code, a unique 8-digit number to unblock the SIM card
• Enter a new PIN code for the attacker-controlled SIM
• Device automatically unlocks

This also means that all an adversary needs to unlock a Pixel
phone is to bring their own PIN-locked SIM card and is in
possession of the card’s PUK code.

“The attacker could just swap the SIM in the victim’s device,
and perform the exploit with a SIM card that had a PIN lock and for
which the attacker knew the correct PUK code,” Schütz said.

An analysis of the source code commits^[4]
made by Google to patch the flaw shows that it’s caused by an
“incorrect system state” introduced as a result of wrongly
interpreting the SIM change event, causing it to entirely dismiss
the lock screen.

“I was not expecting to cause this big of a code change in
Android with this bug,” Schütz concluded.