SB2019120410 - Information disclosure in Windows Hello for Business

The vulnerability allows a local user to gain access to sensitive information.

The vulnerability exists due to improper handling of public keys for Windows Hello for Business (WHfB), when removed from Active Directory.

After a user sets up Windows Hello for Business (WHfB), the WHfB public key is written to the on-premises Active Directory. The WHfB keys are tied to a user and a device that has been added to Azure AD, and if the device is removed, the corresponding WHfB key is considered orphaned. However, these orphaned keys are not deleted even when the device it was created on is no longer present. Any authentication to Azure AD using such an orphaned WHfB key will be rejected. However, some of these orphaned keys could lead to the following security issue in Active Directory 2016 or 2019, in either hybrid or on-premises environments.

An authenticated attacker could obtain orphaned keys created on TPMs that were affected by SB2017101023 (ROCA) to compute their WHfB private key from the orphaned public keys.

Successful exploitation of the vulnerability may allow an attacker to impersonate victim's account with domain using Public Key Cryptography for Initial Authentication (PKINIT).