In Yubico pam-u2f before 1.3.1, local privilege escalation can sometimes occur. This product implements a Pluggable Authentication Module (PAM) that can be deployed to support authentication using a YubiKey or other FIDO compliant authenticators on macOS or Linux. This software package has an issue that allows for an authentication bypass in some configurations. An attacker would require the ability to access the system as an unprivileged user. Depending on the configuration, the attacker may also need to know the user's password.

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.

In Yubico pam-u2f 1.0.7, when configured with debug and a custom debug log file is set using debugfile, that file descriptor is not closed when a new process is spawned. This leads to the file descriptor being inherited into the child process; the child process can then read from and write to it. This can leak sensitive information and also, if written to, be used to fill the disk or plant misinformation.

Yubico pam-u2f 1.0.7 attempts parsing of the configured authfile (default $HOME/.config/Yubico/u2fkeys) as root (unless openasuser was enabled), and does not properly verify that the path lacks symlinks pointing to other files on the system owned by root. If the debug option is enabled in the PAM configuration, part of the file contents of a symlink target will be logged, possibly revealing sensitive information.