A security problem in version 2.4 - 2.7 of Yubico PAM has been found
and patched by Nanakos Chrysostomos <
nan...@wired-net.gr>.
If pam_yubico was configured as 'sufficient' in the PAM configuration
(meaning single factor YubiKey authentication only), and
use_first_pass was NOT used then you could simply press Ctrl+D at the
"Yubikey for `username': " prompt to log in.
At least on Ubuntu 11.04, this did not affect remote logins using SSH
although it did affect `su'.
Get it from
http://code.google.com/p/yubico-pam/downloads/list
or from my PPA (
https://launchpad.net/~fredrikt/+archive/yubico) if
you are using Ubuntu.
/Fredrik