CVE-2021-31924

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the
pam-u2f configuration and the application used, could lead to a local PIN
bypass. This issue does not allow user presence (touch) or cryptographic
signature verification to be bypassed, so an attacker would still need to
physically possess and interact with the YubiKey or another enrolled
authenticator. If pam-u2f is configured to require PIN authentication, and
the application using pam-u2f allows the user to submit NULL as the PIN,
pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this
authentication is successful, the PIN requirement is bypassed.