Post Jailbreak: How To Reset Your iPhone's root Password

How To Change the iPhone's Root Password | iSource

How To Change The iPhone 's Default Admin Account Passwords:

On a Mac:

• Find your iPhone 's IP address so that you know where you need to connect to.  To do this, go to the Settings app > WiFi > tap on the blue arrow to the right-hand side of the WiFi network you 're currently on (the one with a check next to it) > make a note of the IP Address entry listed there.
• On many home WiFi networks the address will be something like 192.168.1.x " so we 'll use that in the command instructions below " remember to use your own IP address when doing this though.
• Use the Terminal app or your favorite replacement for it (I use iTerm) and open a new window
• Type this to connect as root to your iPhone: ssh root@192.168.1.x
• You 'll be prompted for the root user 's current password.  Enter this: alpine
• Type this to start on changing the password for the root user: passwd
• Type the old password (alpine) and new password (twice) as per the instructions above for the iPhone.
• Once you have changed the root user 's password, type this to switch to the mobile user: login mobile
• Type this to start the password change for this user: passwd
• Type the old password (alpine) and new password (twice) as per the instructions above for the iPhone.
• Type this to end your remote session with the iPhone: exit

Done.
On a Windows PC

• Find your iPhone 's IP address so that you know where you need to connect to.  To do this, go to the Settings app > WiFi > tap on the blue arrow to the right-hand side of the WiFi network you 're currently on (the one with a check next to it) > make a note of the IP Address entry listed there.
• On many home WiFi networks the address will be something like 192.168.1.x " so we 'll use that in the command instructions below " remember to use your own IP address when doing this though.
• Use Putty (free to download on the web) or your preferred app to make an ssh connection to the iPhone
• Use 192.168.1.x (your iPhone 's IP address) as the host name or server name to connect to.  Choose ssh as the connection method, SFTP as the protocol, and 22 as the port number.
• Use the username root to connect with and alpine as its password
• When you have connected and have a terminal window open type this to start your password change for the root user: passwd
• Type the old password (alpine) and new password (twice) as per the instructions above for the iPhone.
• Once you have changed the root user 's password, type this to switch to the mobile user: login mobile
• Type this to start the password change for this user: passwd
• Type the old password (alpine) and new password (twice) as per the instructions above for the iPhone.
• Type this to end your remote session with the iPhone: exit
• Done.
  
  As you can see, these are easy and fast steps to take.  If you 're running your iPhone jailbroken and using the SSH service it 's very worthwhile to make these changes to the default passwords.  Even if you do not use SSH, keep in mind that other core iPhone services may have security holes and exploits in future " so the password change is a good idea all the way round.
  If you are using SSH, another good practice is to keep the service always toggled off except when you are using it for file transfers or similar activities, and to get in the habit of shutting it off as soon as you 're finished working with it.  The easiest way to do this is to use the excellent SBSettings app, to have a quick one-tap toggle on/off for SSH and other key services.