User Mode and Privileged Mode Security

 In this lesson, we’ll take a look at how you can secure user mode and privileged (enable) mode. By default, there is no authentication required. If you connect a Cisco console cable to your switch or router, here’s what happens:

Switch con0 is now available

Press RETURN to get started.

Switch>

Once you press the enter button, we end up in user mode right away. There’s no password or anything. The same thing applies to the enable mode:

Switch>enable
Switch#

We have full access right away. This is something you might want to change, which is what I’ll explain in this lesson.

User Mode Security

Let’s start with user mode.

Simple Password

The most simple option to protect user mode is to add a password. Here’s how to do this:

Switch(config)#line console 0

First, we need to enter the console settings. Here’s where we have to add two commands:

Switch(config-line)#password cisco          
Switch(config-line)#login

We configure a password (cisco) and use the login command to tell Cisco IOS to prompt for this password. Next time you open the console, this will happen:

Switch con0 is now available

Press RETURN to get started.

User Access Verification

Password: 
Switch>

The CLI will ask you for the password. At least we have some form of authentication but we can do better…

Username and Password

Instead of a single password, it’s also possible to use usernames and passwords instead. This is a better option if you have multiple people that need to access your router or switch. Here’s how to do this:

Switch(config)#line console 0
Switch(config-line)#login local
Switch(config-line)#exit

Switch(config)#username admin password cisco

Under the console settings, we use the login local command to tell the switch to refer to a local database of usernames and passwords for authentication. In the global config, we create a username “admin” with password “cisco”.

Next time you open the console, here’s what you see:

Switch con0 is now available

Press RETURN to get started.

User Access Verification

Username: admin
Password: 
Switch>

The switch asks for our username and password.

Enable Mode Security

What about enable mode / privileged mode? We can also add a password there. You need to do this from the configuration mode:

Switch#configure terminal 

Now we can set a password for enable mode:

Switch(config)#enable password cisco

Let’s see if our password “cisco” works. Let’s get out of enable mode:

Switch#disable

And jump right back in:

Switch>enable
Password:

The switch now asks for the password.

Password Encryption

In the examples above, we used passwords but there is one problem…they all show up in clear text in our configuration. Take a look below:

Switch#show running-config | include password
no service password-encryption
enable password cisco
username admin password 0 cisco

It’s all clear text. If someone steals one of your switches or routers, they will have your passwords. If you ever backup your configuration and forget to remove the passwords, same problem.

Cisco IOS has a command that lets you encrypt all clear text passwords in your configuration. Here’s how:

Switch(config)#service password-encryption

The service password-encryption command will encrypt every password that is plain text. Here you can see the result:

Switch#show running-config | include password
service password-encryption
enable password 7 13061E010803
username admin password 7 110A1016141D

Now you might get a warm fuzzy feeling that everything is encrypted but in reality, this is a very poor (broken) encryption algorithm. There are websites that let you decrypt these encrypted strings on the fly. If you want to try this, here’s one of those websites.

We need something stronger…

Secret

Cisco IOS supports something called a secret as an alternative to the password. Let’s try this for the enable mode:

Switch(config)#enable secret ?
  0      Specifies an UNENCRYPTED password will follow
  5      Specifies a MD5 HASHED secret will follow
  8      Specifies a PBKDF2 HASHED secret will follow
  9      Specifies a SCRYPT HASHED secret will follow
  LINE   The UNENCRYPTED (cleartext) 'enable' secret
  level  Set exec level password

Above you can see this switch supports MD5, PBKDF2 and SCRYPT hashes. Older IOS devices only support MD5 authentication.

Let’s give this a try:

Switch(config)#enable secret cisco

Our secret will be “cisco”. Let’s see what we find in the configuration:

Switch#show running-config | include secret
enable secret 5 $1$CANW$U9Y8O6KeFhrFR4l1Qo07h/

You now find an MD5 hash in the configuration. The “5” that you see behind “enable secret” is the algorithm that we use, 5 means MD5.

MD5 is not considered secure nowadays. It’s very easy to brute force simple passwords. For example, try this website for the MD5 hash that was created for my secret “cisco”. It will only take a few seconds to recover.

Let’s try one of the other algorithms that are considered secure nowadays. Here’s how you can select the algorithm for the enable mode:

Switch(config)#enable algorithm-type ?
  md5     Encode the password using the MD5 algorithm
  scrypt  Encode the password using the SCRYPT hashing algorithm
  sha256  Encode the password using the PBKDF2 hashing algorithm

Let’s try the PBKDF2 (SHA256) hashing algorithm:

Switch(config)#enable algorithm-type sha256 secret cisco

When we look at our configuration, we’ll see the new hash:

Switch#show running-config | include secret
enable secret 8 $8$dvX/fx/FJ0Snk2$HhqrOUaEtBgk4zJvG2IQuAJNUicZmmELelC/L6.Fcl2

The “8” behind “enable secret” refers to the PBKDF2 hashing algorithm that we used.

In the example above I changed the hashing algorithm for the enable mode but we can also do this for usernames. Here’s an example:

Switch(config)#username rene algorithm-type sha256 secret cisco

My username now uses SHA256 as well for password “cisco”. Here’s what it looks like:

Switch#show running-config | include rene    
username rene secret 8 $8$dyzsAmZjA3w.aY$YBZn8LBI6CK04ij5ZmqQ/88OrFdc3jzGb6v7SSQI0cw

Make sure you use strong passwords. No matter what hashing algorithm you use, weak passwords like “cisco” are easily recovered.

External Authentication Servers

Configuring usernames and secrets on your Cisco IOS devices is a good practice but one issue we have is scalability. If you have a network with multiple devices, you will have to configure your usernames/secrets on all devices. If you change your password, you have to do it on all devices.

In larger networks, we typically use authentication servers called RADIUS or TACACS+ servers. On these servers, we configure our usernames. When someone tries to access the console or enable mode on one of your switches or routers, they check the credentials on the authentication server.

This allows you to keep your authentication centralized. This is something we will cover in other lessons.

Conclusion

You have now learned how to protect the user and enable mode of your Cisco IOS devices. Make sure you use “secret” instead of plain text passwords and if possible, use a stronger hashing algorithm than the default MD5.