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Duo RADIUS Two-Factor Authentication with Password Reset for Cisco ASA SSL VPNs

Last Updated: April 19th, 2022

Duo integrates with your Cisco ASA VPN to add two-factor authentication to any VPN login.

Overview

These Cisco AnyConnect RADIUS instructions support push, phone call, or passcode authentication for AnyConnect desktop and mobile client connections that use SSL encryption. This configuration does not feature the interactive Duo Prompt for web-based logins, but does capture client IP informations for use with Duo policies, such as geolocation and authorized networks.

This configuration uses a Duo-only RADIUS configuration, which supports separate primary and secondary authentication configurations in sequence for user login. In this configuration you can keep your existing ASA AAA primary LDAP or RADIUS authentication server in place, and add the Duo Authentication Proxy as a secondary authentication server for two-factor authentication after primary authentication succeeds. User access is granted after both primary and secondary authentication success.

This configuration also allows for your VPN device to handle primary password resets directly against the RADIUS or LDAP user store (note that these password changes will occur before Duo 2FA).

The SAML VPN instructions feature inline enrollment and the interactive Duo Prompt for both web-based VPN logins and AnyConnect 4.6+ client logins. This deployment option features Duo Single Sign-On, our cloud-hosted SAML 2.0 identity provider. Primary and Duo secondary authentication occur at the Duo SSO identity provider, not at the ASA itself. Duo SSO also includes support for password resets when using Active Directory as the authentication source.

Please refer to the Duo for Cisco AnyConnect VPN with ASA or Firepower overview to learn more about the different options for protecting ASA logins with Duo MFA.

Before starting, make sure that Duo is compatible with your Cisco ASA device. Log on to your Cisco ASDM interface and verify that your Cisco ASA firmware is version 8.3 or later.

Connectivity Requirements

This application communicates with Duo's service on TCP port 443. Firewall configurations that restrict outbound access to Duo's service with rules using destination IP addresses or IP address ranges aren't recommended, since these may change over time to maintain our service's high availability. If your organization requires IP-based rules, please review this Duo KB article.

First Steps

Before moving on to the deployment steps, it's a good idea to familiarize yourself with Duo administration concepts and features like options for applications, available methods for enrolling Duo users, and Duo policy settings and how to apply them. See all Duo Administrator documentation.

You should already have a working primary authentication configuration for your Cisco ASA SSL VPN users before you begin to deploy Duo.

To integrate Duo with your Cisco ASA SSL VPN, you will need to install a local Duo proxy service on a machine within your network. This Duo proxy server will receive incoming RADIUS requests from your Cisco ASA SSL VPN and then contact Duo's cloud service for secondary authentication.

If you are already running a Duo Authentication Proxy server in your environment, you can use that existing host for additional applications, appending the new configuration sections to the current config. You don't have to set up a new Authentication Proxy server for each application you create. However, there are some cases where it might make sense for you to deploy a new proxy server for a new application, like if you want to co-locate the Duo proxy with the application it will protect in the same data center.

If you will set up a new Duo server, locate (or set up) a system to host the Duo Authentication Proxy installation. The proxy supports these operating systems:

  • Windows Server 2012 or later (Server 2016+ recommended)
  • CentOS 7 or later (CentOS 8+ recommended)
  • Red Hat Enterprise Linux 7 or later (RHEL 8+ recommended)
  • Ubuntu 16.04 or later (Ubuntu 18.04+ recommended)
  • Debian 7 or later (Debian 9+ recommended)

See detailed Authentication Proxy operating system performance recommendations in the Duo Authentication Proxy Reference.

Then you'll need to:

  1. Sign up for a Duo account.
  2. Log in to the Duo Admin Panel and navigate to Applications.
  3. Click Protect an Application and locate Cisco RADIUS VPN in the applications list. Click Protect to get your integration key, secret key, and API hostname. You'll need this information to complete your setup. See Protecting Applications for more information about protecting applications in Duo and additional application options.
Treat your secret key like a password

The security of your Duo application is tied to the security of your secret key (skey). Secure it as you would any sensitive credential. Don't share it with unauthorized individuals or email it to anyone under any circumstances!

Install the Duo Authentication Proxy

If you will reuse an existing Duo Authentication Proxy server for this new application, you can skip the install steps and go to Configure the Proxy.

The Duo Authentication Proxy can be installed on a physical or virtual host. We recommend a system with at least 1 CPU, 200 MB disk space, and 4 GB RAM (although 1 GB RAM is usually sufficient). See additional Authentication Proxy performance recommendations in the Duo Authentication Proxy Reference.

  1. Download the most recent Authentication Proxy for Windows from https://dl.duosecurity.com/duoauthproxy-latest.exe. Note that the actual filename will reflect the version e.g. duoauthproxy-5.7.0.exe. View checksums for Duo downloads here.
  2. Launch the Authentication Proxy installer on the target Windows server as a user with administrator rights and follow the on-screen prompts.

    When installing, you can choose whether or not you want to install the Proxy Manager. The Proxy Manager is a Windows utility that helps you edit the Duo Authentication Proxy configuration, determine the proxy's status, and start or stop the proxy service. Learn more about using the Proxy Manager. Installing the Proxy Manager adds about 100 MB to the installed size.

    If you do not want to install the Proxy Manager, you may deselect it on the "Choose Components" installer screen before clicking Install.

Silent Install

To perform a silent install on Windows, issue the following from an elevated command prompt after downloading the installer (replacing version with the actual version you downloaded):

duoauthproxy-version.exe /S

Append /exclude-auth-proxy-manager to install silently without the Proxy Manager:

duoauthproxy-version.exe /S /exclude-auth-proxy-manager
  1. Ensure that Perl and a compiler toolchain are installed. On most recent RPM-based distributions — like Fedora, RedHat Enterprise, and CentOS — you can install these by running (as root):

    $ yum install gcc make libffi-devel perl zlib-devel diffutils

    On Debian-derived systems, install these dependencies by running (as root):

    $ apt-get install build-essential libffi-dev perl zlib1g-dev

    If SELinux is present on your system and you want the Authentication Proxy installer to build and install its SELinux module, include selinux-policy-devel in the dependencies:

    $ yum install gcc make libffi-devel perl zlib-devel diffutils selinux-policy-devel
    $ apt-get install build-essential libffi-dev perl zlib1g-dev selinux-policy-devel
  2. Download the most recent Authentication Proxy for Unix from https://dl.duosecurity.com/duoauthproxy-latest-src.tgz. From the command line you can use curl or wget to download the file, like $ wget --content-disposition https://dl.duosecurity.com/duoauthproxy-latest-src.tgz. Depending on your download method, the actual filename may reflect the version e.g. duoauthproxy-5.7.0-src.tgz. View checksums for Duo downloads here.

  3. Extract the Authentication Proxy files and build it as follows:

    $ tar xzf duoauthproxy-5.7.0-src.tgz
    $ cd duoauthproxy-version-src
    $ make
  4. Install the authentication proxy (as root):

    $ cd duoauthproxy-build
    $ ./install

    Follow the prompts to complete the installation. The installer creates a user to run the proxy service and a group to own the log directory and files. You can accept the default user and group names or enter your own.

    If SELinux is present on the target server, the Duo installer will ask you if you want to install the Authentication Proxy SELinux module. Your selection affects whether systemd can start the Authentication Proxy after installation.

    If you choose to install the Authentication Proxy SELinux module and the dependency selinux-policy-devel is not present then the installer fails to build the module.

    SELinux Mode Default Response Result
    Enforcing Yes Choose 'yes' to install the Authentication Proxy's SELinux module. This permits start of the Authentication Proxy service by systemd. If you choose 'no' then the SELinux module is not installed, and systemd cannot start the Authentication Proxy service.
    Permissive No Choose 'no' to decline install of the Authentication Proxy's SELinux module. The Authentication Proxy service can be started by systemd. However, if you change SELinux from permissive to enforcing mode after installing the Duo proxy, systemd can no longer start the Authentication Proxy service. If you plan to enable SELinux enforcing mode later, you should choose 'yes' to install the Authentication Proxy SELinux module now.
Silent Install

To install the Duo proxy silently with the default options, use the following command:

sudo ./duoauthproxy-build/install --install-dir /opt/duoauthproxy --service-user duo_authproxy_svc --log-group duo_authproxy_grp --create-init-script yes

Append --enable-selinux=yes|no to the install command to choose whether to install the Authentication Proxy SELinux module.

Configure the Proxy

After the installation completes, you will need to configure the proxy.

The Duo Authentication Proxy configuration file is named authproxy.cfg, and is located in the conf subdirectory of the proxy installation. With default installation paths, the proxy configuration file will be located at:

Operating System Authentication
Proxy Version
Path
Windows v5.0.0 and later C:\Program Files\Duo Security Authentication Proxy\conf\authproxy.cfg
Windows v4.0.2 and earlier C:\Program Files (x86)\Duo Security Authentication Proxy\conf\authproxy.cfg
Linux All /opt/duoauthproxy/conf/authproxy.cfg

Note that as of v4.0.0, the default file access on Windows for the conf directory is restricted to the built-in Administrators group during installation.

The configuration file is formatted as a simple INI file. Section headings appear as:

[section]

Individual properties beneath a section appear as:

name=value

The Authentication Proxy may include an existing authproxy.cfg with some example content. For the purposes of these instructions, however, you should delete the existing content and start with a blank text file.

Duo Authentication Proxy Manager

The Duo Authentication Proxy Manager is a Windows utility for managing the Authentication Proxy installation on the Windows server where you install the Authentication Proxy. The Proxy Manager comes with Duo Authentication Proxy for Windows version 5.6.0 and later.

The Proxy Manager cannot manage remote Duo Authentication Proxy servers, nor can you install the Proxy Manager as a stand-alone application. There is no Proxy Manager available for Linux. The Proxy Manager only functions as part of a local Duo Authentication Proxy installation on Windows servers.

Learn more about using the Proxy Manager in the Duo Authentication Proxy Reference before you continue.

To launch the Proxy Manager utility:

  • Open the Start Menu and go to Duo Security.
  • Click the Duo Authentication Proxy Manager icon to launch the application. You must have administrative privileges on the Windows server and accept the prompt for elevation.
  • The Proxy Manager launches and automatically opens the %ProgramFiles%\Duo Security Authentication Proxy\conf\authproxy.cfg file for editing.

Use the Proxy Manager editor on the left to make the authproxy.cfg changes in these instructions. As you type into the editor, the Proxy Manager will automatically suggest configuration options. Accepting these suggestions helps make sure you use the correct option syntax.

As you follow the instructions on this page to edit the Authentication Proxy configuration, you can click Validate to verify your changes (output shown on the right).

When you complete the Authentication Proxy configuration steps in this document, you can use the Save button to write your updates to authproxy.cfg, and then use the authproxy.cfg button to start the Authentication Proxy service before continuing on to the next configuration steps.

If you do not use the Proxy Manager to edit your configuration then we recommend using WordPad or another text editor instead of Notepad when editing the config file on Windows.

Configure the Proxy for Duo Only Authentication

At the top of your authproxy.cfg, create a [duo_only_client] section. This section has no additional parameters to configure.

[duo_only_client]

When using the [duo_only_client] configuration, the Authentication Proxy will ignore primary credentials and perform Duo factor authentication only.

Configure the Proxy for Your Cisco ASA SSL VPN

Next, you need to set up the Authentication Proxy to work with your Cisco ASA SSL VPN. Create a [radius_server_duo_only] section and add the properties listed below. If you've already set up the Duo Authentication Proxy for a different RADIUS Duo-only application, append a number to the section header to make it unique, like [radius_server_duo_only2].

Required

ikey

Your integration key.

skey

Your secret key.

api_host

Your API hostname (e.g. "api-XXXXXXXX.duosecurity.com").

radius_ip_1

The IP address of your Cisco ASA SSL VPN.

radius_secret_1

A secret to be shared between the proxy and your Cisco ASA SSL VPN. If you're on Windows and would like to encrypt this secret, see Encrypting Passwords in the full Authentication Proxy documentation.

client

The mechanism that the Authentication Proxy should use to perform primary authentication. This should correspond with a "client" section elsewhere in the config file.

duo_only_client

Do not perform primary authentication. Make sure you have a [duo_only_client] section configured.

This parameter is optional if you only have one "client" section. If you have multiple, each "server" section should specify which "client" to use.

Optional

port

The port on which to listen for incoming RADIUS Access Requests. If you have multiple RADIUS server sections you should use a unique port for each one.

Default: 1812.

failmode

Either "safe" or "secure":

"safe"

In the event that Duo's service cannot be contacted, users' authentication attempts will be permitted if primary authentication succeeds. This is the default.

"secure"

In the event that Duo's service cannot be contacted, all users' authentication attempts will be rejected.

radius_ip_2

The IP address of your second Cisco ASA SSL VPN, if you have one. You can specify additional devices as as radius_ip_3, radius_ip_4, etc.

radius_secret_2

The secrets shared with your second Cisco ASA SSL VPN, if using one. You can specify secrets for additional devices as radius_secret_3, radius_secret_4, etc. If you're on Windows and would like to encrypt this secret, see Encrypting Passwords in the full Authentication Proxy documentation.

A completed config file for radius_server_duo_only with no primary authenticator should look something like:

[duo_only_client]
 
[radius_server_duo_only]
ikey=DIXXXXXXXXXXXXXXXXXX
skey=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
api_host=api-XXXXXXXX.duosecurity.com
failmode=safe
radius_ip_1=5.6.7.8
radius_secret_1=radiussecret1
port=1812

Make sure to save your configuration file in your text editor — or validate and save in the Proxy Manager for Windows — when you're finished making changes.

Note

View video guides for proxy deployment at the Authentication Proxy Overview or see the Authentication Proxy Reference for additional configuration options.

Start the Proxy

If you installed the Duo Authentication Proxy Manager utility (available with 5.6.0 and later), click the Start Service button at the top of the Proxy Manager window to start the service.

To start the service from the command line, open an Administrator command prompt and run:

net start DuoAuthProxy

Alternatively, open the Windows Services console (services.msc), locate "Duo Security Authentication Proxy Service" in the list of services, and click the Start Service button.

Authentication Proxy v5.1.0 and later includes the authproxyctl executable, which shows the connectivity tool output when starting the service. The installer adds the Authentication Proxy C:\Program Files\Duo Security Authentication Proxy\bin to your system path automatically, so you should not need to specify the full path to authproxyctl to run it.

From an administrator command prompt run:

authproxyctl start

If the service starts successfully, Authentication Proxy service output is written to the authproxy.log file, which can be found in the log subdirectory.

If you see an error saying that the "service could not be started", open the Application Event Viewer and look for an Error from the source "DuoAuthProxy". The traceback may include a "ConfigError" that can help you find the source of the issue.

Stop and restart the Authentication Proxy service by either clicking the Restart Service button in the Duo Authentication Proxy Manager or the Windows Services console or issuing these commands from an Administrator command prompt:

net stop DuoAuthProxy & net start DuoAuthProxy

To stop and restart the Authentication Proxy using authproxyctl, from an administrator command prompt run:

authproxyctl restart

Open a root shell and run:

# /opt/duoauthproxy/bin/authproxyctl start

To ensure the proxy started successfully, run:

# /opt/duoauthproxy/bin/authproxyctl status

Authentication Proxy service output is written to the authproxy.log file, which can be found in the log subdirectory.

To stop and restart the Authentication Proxy, open a root shell and run:

# /opt/duoauthproxy/bin/authproxyctl restart

If you modify your authproxy.cfg configuration after initial setup, you'll need to stop and restart the Duo Authentication Proxy service or process for your change to take effect.

Configure Your Cisco ASA

Add the Duo RADIUS server

  1. Navigate to AAA/Local UsersAAA Server Groups, click Add, and fill out the form:

    Setting Value
    AAA Server Group Duo-RADIUS
    Protocol RADIUS

    Add AAA Server Group

    Click OK to create the new AAA server group.

  2. Select the Duo-RADIUS group you just added. In the Add AAA Server dialog, enter the following information:

    Setting Value
    Interface Name The ASA interface where your Duo Authentication Proxy can be reached.
    Server Name or IP Address The hostname or IP address of your Duo Authentication Proxy.
    Timeout 60 seconds should be sufficient to complete authentication; see the FAQ item about timeouts.
    Server Accounting Port 1813 (Technically this setting does not matter because the Duo Authentication Proxy does not support RADIUS Accounting).
    Retry Interval 10 seconds
    Server Secret Key Shared Secret used in Authentication Proxy configuration.
    Microsoft CHAPv2 Capable Unchecked

    New RADIUS Server

    Click OK, and then OK to save the new server.

  3. You can verify connectivity to the Duo RADIUS server now. With the Duo AAA server group you just created selected, click the Test button.

  4. On the "Test AAA Server" form, select Authentication.

  5. Enter the username of user that exists in Duo and has a valid authentication device (like a phone or token).

  6. In the "Password" field, enter a Duo factor name for that user, such as the factor name push to send a Duo Push request to the first activated phone attached to the user or phone to call the user, or type in a numeric token passcode Duo bypass code. Click OK.

  7. If the user is set up for Duo Push or phone call authentication, approve the Duo authentication request.

  8. A new form pops up letting you know if the test was successful or failed.

Add Duo as a Secondary SSL VPN Authentication Method

  1. Navigate to Clientless SSL VPN AccessConnection Profiles
  2. Select the connection profile to which you want to add Duo Authentication near the bottom and click Edit. This can be the default connection profile "DefaultWEBVPNGroup" or another existing connection profile.
  3. Choose Secondary Authentication (under Advanced) from the left menu.
  4. Select Duo-RADIUS from the Server Group list.
  5. Uncheck the Use LOCAL if Server Group fails check box.
  6. Check the Use primary username check box.
  7. Click OK.
  8. Click Apply.

Click Save to write all changes to the ASA device memory.

Configure AnyConnect Timeout

It's a good idea to increase the AnyConnect Authentication Timeout so that users have enough time to use Duo Push or phone callback.

  1. Navigate to ConfigurationRemote Access VPNNetwork (Client) AccessAnyConnect Client Profile and Click Edit.
  2. In the left menu, navigate to Preferences (Part 2).
  3. Scroll to the bottom of the page and modify the Authentication Timeout (seconds) setting to 60 seconds. AnyConnect Timeout
  4. Click OK.
  5. Click Apply to activate the new AnyConnect Client settings.
  6. Click Save to write this change to the ASA device memory.

This timeout setting will take effect after each client successfully logs into the VPN after applying the new profile.

Test Your Setup

Launch the AnyConnect client and select the VPN profile that now uses Duo RADIUS authentication.

Users see a “Second Password” field when using the AnyConnect client, which cannot be left blank.

Cisco AnyConnect Client Prompt

Enter the primary username and password, and a Duo factor option as the second password. Choose from:

push Perform Duo Push authentication
You can use Duo Push if you've installed and activated Duo Mobile on your device.
phone Perform phone callback authentication.
sms Send a new batch of SMS passcodes.
Your authentication attempt will be denied. You can then authenticate with one of the newly-delivered passcodes.
A numeric passcode Log in using a passcode, either generated with Duo Mobile, sent via SMS, generated by your hardware token, or provided by an administrator. Examples: "123456" or "2345678"

You can also specify a number after the factor name if you have more than one device enrolled (as the automatic push or phone call goes to the first capable device attached to a user). So you can enter push2 or phone2 if you have two phones enrolled and you want the authentication request to go to the second phone.

Once you approve the Duo authentication request (or if you appended a valid passcode to your password for MFA), the AnyConnect client is connected to the VPN.

Logging into the web-based VPN via browser sends an automatic Duo request via push or phone call. You can also append a different Duo factor name or passcode to your password in the browser, just like you can in AnyConnect.

Troubleshooting

Need some help? Review troubleshooting tips for the Authentication Proxy and try the connectivity tool included with Duo Authentication Proxy 2.9.0 and later to discover and troubleshoot general connectivity issues.

Also take a look at the Cisco Frequently Asked Questions (FAQ) page or try searching our Cisco Knowledge Base articles or Community discussions. For further assistance, contact Support.

Network Diagram

  1. Primary authentication initiated to Cisco ASA
  2. Primary authentication using Active Directory or RADIUS
  3. Cisco ASA sends secondary authentication request to the Duo Authentication Proxy
  4. Duo Authentication Proxy connection established to Duo Security over TCP port 443
  5. Secondary authentication via Duo Security’s service
  6. Duo authentication proxy receives authentication response
  7. Cisco ASA VPN access granted