Wednesday, 1 November 2017

Implementing 802.1X with a Cisco 2960, FreeRADIUS and Windows 7 / 10

802.1X: 802.1X allows you to securely authenticate devices connecting to a network - while often employed in wireless networks it is also often used along side wired ones as well. A typical transaction will involve the authenticator (the switch in this case) sending a EAP message to the supplicant (the client workstation in this case) and will then send back an EAP response.

For this lab we will be focusing on wired networks and will be attempting to address the problem of visiting employees from company A from plugging in their equipment into Company B's infrastructure.

To start we will need the following components:

- A client machine running Windows 7 / 10 (192.168.20.2/24)
- A Cisco 2960 switch with IOS > 15 (192.168.20.1/24)
- A linux box running FreeRadius (192.168.20.254/24)

Switch

So let's firstly look at the switch portion - we'll configure dot1x and radius on the switch:

conf t
aaa new-model

radius server dot1x-auth-serv
 address ipv4 192.168.20.2 auth-port 1812 acct-port 1813
 timeout 3
 key (7) <sharedkey>

aaa group server radius dot1x-auth
server name dot1x-auth-serv

aaa authentication dot1x default group dot1x-auth
aaa accounting dot1x default start-stop group dot1x-auth
aaa authorization network default group dot1x-auth

and proceed by enabling dot1x:

dot1x system-auth-control

and we'll then enable it on the relevant ports:

int range gi0/1-5
switchport mode access
authentication port-control auto
dot1x pae authenticator

FreeRADIUS Server

We'll continue on the server by installing radiusd:

sudo yum install freeradius

and then use samba to communicate with the domain:

sudo yum install samba samba-common samba-common-tools krb5-workstation openldap-clients policycoreutils-python

(We are not actually setting up a samba server - instead just using some of the tools that are provided with it!)

vi /etc/samba/smb.conf


[global]
        workgroup = <domain-name>
        security = user
        winbind use default domain = no
        password server = <ad-server>
        realm = <domain-name>
        #passdb backend = tdbsam


[homes]
        comment = Home Directories
        valid users = %S, %D%w%S
        browseable = No
        read only = No
        inherit acls = Yes

and then edit the kerberos configuration:

vi /etc/krb5.conf

 Configuration snippets may be placed in this directory as well
includedir /etc/krb5.conf.d/

[logging]
 default = FILE:/var/log/krb5libs.log
 kdc = FILE:/var/log/krb5kdc.log
 admin_server = FILE:/var/log/kadmind.log

[libdefaults]
 dns_lookup_realm = false
 ticket_lifetime = 24h
 renew_lifetime = 7d
 forwardable = true
 rdns = false
 # default_realm = EXAMPLE.COM
 default_ccache_name = KEYRING:persistent:%{uid}

[realms]
 domain.com = {
  kdc = pdc.domain.com
 }

[domain_realm]
 .domain.com = DOMAIN.COM
 domain.com = DOMAIN.COM

and then modify NSS to ensure that it performs lookups using windbind:

vi /etc/nsswitch.conf

passwd:     files winbind
shadow:     files winbind
group:      files winbind
protocols:  files winbind
services:   files winbind
netgroup:   files winbind
automount:  files winbind

ensure samba starts on boot and restart the system:

sudo systemctl enable smb
sudo systemctl enable winbind
sudo shutdown -r now

Now join the domain with:

net join -U <admin-user>

and attempt to authenticate against a user with:

wbinfo -a <username>%<password>

should return something like:

Could not authenticate user user%pass with plaintext password
challenge/response password authentication succeeded

We also need to ensure NTLM authentication works (as this is what is used with FreeRadius):

ntlm_auth --request-nt-key --domain=<domain-name> --username=<username>

should return:

NT_STATUS_OK: Success (0x0)

(Providing the account is in good order e.g. not locked etc.)

The 'ntlm_auth' program needs access to the 'winbind_privileged' directory - so we should ensure that the user running the radius server is within the 'wbpriv' group:

usermod -a -G wbpriv radiusd

and then proceed to install and setup freeradius:

sudo yum install freeradius
sudo systemctl enable radiusd

mv /etc/raddb/clients.conf /etc/raddb/clients.conf.orig
vi /etc/raddb/clients.conf

and add the following:

client <switch-ip> {
        secret                = <secret-key>
        shortname             = <switch-ip>
        nastype               = cisco
}

We'll now configure mschap:

vi /etc/raddb/mods-enabled/mschap

and ensure the following is set:

with_ntdomain_hack = yes

ntlm_auth = "/usr/bin/ntlm_auth --request-nt-key --username=%{%{Stripped-User-Name}:-%{%{User-Name}:-None}} --challenge=%{%{mschap:Challenge}:-00} --nt-response=%{%{mschap:NT-Response}:-00}"

and the EAP configuration:

sudo vi /etc/raddb/mods-available/eap

Search for the following line:

tls-config tls-common

and uncomment:

random_file = /dev/urandom

Make sure your firewall is setup correctly:

sudo iptables -A INPUT -p udp -m state --state NEW -m udp --dport 1812 -j ACCEPT
sudo iptables -A INPUT -p udp -m state --state NEW -m udp --dport 1813 -j ACCEPT

and then test the configuration by running FreeRadius in test mode:

sudo radiusd -XXX

Then on the Windows 7 / 10 client workstation ensure that the 'Wired AutoConfig' service has been started (and has also been set to 'Automatic'.)

On the relevant NIC properties ensure that 'Enable 802.1X authentication' has been enabled:


Within Windows 10 you should not need to perform this - however it's always best to check the defaults just in case!

If you are not using a certificate ensure that the 'Verify the server's identity by validating the certificate' is unchecked as below (within the PEAP Settings):



Click 'Configure...' next to 'Secured password (EAP-MSCHAP v2) and ensure that 'Automatically use my Windows logon name and password' is ticked.

Finally hit 'OK' and back on the 'Authentication' tab - click on 'Additional settings...' and ensure 'Specify authentication mode' is ticked and is set to 'User authentication'.

We can now attempt to plug the client into the switch and with any luck we will obtain network access!


Sources

https://documentation.meraki.com/MS/Access_Control/Configuring_802.1X_Wired_Authentication_on_a_Windows_7_Client

http://wiki.freeradius.org/guide/freeradius-active-directory-integration-howto

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