Debian Linux Security Advisory 3299-1 – Johan Olofsson discovered an authentication bypass vulnerability in Stunnel, a program designed to work as an universal SSL tunnel for network daemons. When Stunnel in server mode is used with the redirect option and certificate-based authentication is enabled with “verify = 2” or higher, then only the initial connection is redirected to the hosts specified with “redirect”. This allows a remote attacker to bypass authentication.