How to reset the enable password on an ASA 5505:
The following procedure worked for me to reset the enable password.
Connect to serial port – typically 9600,8,N,1. On my MacBook Pro, I use a Keyspan USB-Serial adapter, so my command line is:
screen /dev/tty.USA19Hfd13P1.1 9600,8
You can eventually use <ctrl-A><ctrl-\> to kill the screen session.
Power on the device.
When it prompts to interrupt boot sequence, do so (press ESC).
It should prompt
rommon #0> confreg
Should show something like:
Current Configuration Register: 0×00000001
boot default image from Flash
Do you wish to change this configuration? y/n [n]:
Press n (don’t change)
We can have the ASA boot a default config with no password by setting register flags 0×41, so do this:
rommon #2> confreg 0×41
rommon #2> reboot
You now can login as the password has been removed (use <return> as the password). Be sure to set the enable password with:
enable password new-password-here
Ensure you either use the config-register command or interrupt the boot sequence again and reset the boot flags back to 0×1, otherwise the boot loader will continue to boot the default configuration – ignoring your configuration.