How to log into any backdoored Juniper firewall – <<< %s(un='%s') = %u

the string is actually used during login checks. When the magic text is presented as a password over SSH or Telnet, the firmware grants total access to the equipment: regardless of the username given, it allows anyone to bypass authentication, and the password is hardwired into the operating system.

Source: How to log into any backdoored Juniper firewall – hard-coded password published