ASA-2019-00653 – OpenBSD: Local privilege escalation via S/Key and YubiKey

OpenBSD, in a non-default configuration where S/Key or YubiKey authentication is enabled, allows local users to become root by leveraging membership in the auth group. This occurs because root's file can be written to /etc/skey or /var/db/yubikey, and need not be owned by root.

ASA-2019-00322 – pam-u2f: Symlink attack on u2f_keys leading to possible information leak

The file `$HOME/.config/Yubico/u2f_keys` is blindly followed by the PAM module. It can be a symlink pointing to an arbitrary file. The PAM module only rejects non-regular files and files owned by other users than root or the to-be-authenticated user. Even these checks are only made after open()'ing the file, which may already trigger certain logic in the kernel that is otherwise not reachable to regular users.

ASA-2019-00321 – pam-u2f: debug_file file descriptor leak

If the `debug` and `debug_file` options are set then the opened debug file will be inherited to the successfully authenticated user's process. Therefore this user can write further information to it, possibly filling up a privileged file system or manipulating the information found in the debug file.