Microsoft Windows Hello Fingerprint authentication was evaluated for security over its fingerprint sensors embedded in laptops.
This led to the discovery of multiple vulnerabilities that would allow a threat actor to bypass the Windows Hello Authentication completely.
The research was conducted on three laptops, which were Dell Inspiron 15, Lenovo ThinkPad T14, and Microsoft Surface Pro Type Cover with Fingerprint ID (for Surface Pro 8 /X).Â
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Concept of the Vulnerability
Match on Chip
According to the reports shared with Cyber Security News, this vulnerability is based on the concept of “match on chip” type sensors. Microsoft eliminated the method of storing “fingerprint templates” on the host.Â
Instead, the fingerprint templates are now stored on-chip, which potentially reduces the privacy concerns of fingerprint exfiltration from the host in case the host is compromised.
However, this method also has a drawback as it does not prevent a malicious sensor from spoofing a legitimate sensor’s communication with the host, which can spoof an authorized and authenticated user.
Secure Device Connection Protocol (SDCP)
Microsoft developed the SDCP to secure the biometrics and fingerprint sensors.
This protocol consists of a set of standards and a secure communications protocol with goals such as ensuring the fingerprint device is trusted and healthy, and the input is protected between the fingerprint device and the host.
Secure Boot
Devices that support SDCP have a non-updatable bootloader in ROM (secure bootloader), which acts as the device’s root of trust.
Additionally, Microsoft issues a model-specific certificate and private key, which is confidential. However, it is used to sign the public key in a device-specific key pair embedded into the ROM.
Secure Connection BootStrap
This secure connection is authenticated and used to transmit the device’s attestation, which could allow the host to know that it is communicating with a valid device.
Furthermore, it is also used for additional biometric operations like new fingerprint enrolment and authentication.
Targets and Results
The first target was Dell Inspiron, which supports Windows Hello and SDCP. It has been discovered that when enrolling the fingerprints through Windows, it follows the process specified in the SDCP specification.
To bypass security, the initial process was to find the enrolled fingerprints. This was done by setting up a Wireshark dissector and checking the queries to the sensor from the Windows Login Screen.Â
This reveals known fingerprints and IDs that can be used to authenticate the machine. As this operation is unauthenticated, it leaks this information by design.
Exploitation
To bypass this security, researchers booted with Linux and enumerated the valid fingerprint IDs.
After this, they enrolled a new fingerprint using a valid fingerprint ID and made a Man-in-the-Middle (MitM) attack between the host and the sensor. Proceeding further, they booted with Windows, intercepted, and rewrote the configuration packet using MitM.Â
After performing this operation, researchers tried to log in as a legitimate user with the new fingerprint.
The exploitation was successful, and they were able to bypass the Windows Login security feature. Other attack methods were related to USB MitM and Custom TLS attacks.
A complete report about the attack methods has been published, providing detailed information about the attack scenario, method of exploitation, and other information.
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