Step by Step Guide for Configuration of Yubico PAM module to provide single factor YubiKey OTP authentication for RADIUS server.
The purpose of this document is to guide readers through the configuration steps to enable single factor authentication using YubiKey and RADIUS server on Linux platform. This document assumes that the reader has advance knowledge and experience in Linux system administration, particularly how to configure PAM authentication mechanism on a Linux platform.
Successful configuration of the Yubico PAM module to support single factor authentication for RADIUS requires following prerequisites:
Operating System: Any Unix operating system which supports PAM (Pluggable Authentication Module) (http://www.kernel.org/pub/linux/libs/pam/)
Complier : GNU GCC complier (http://gcc.gnu.org/)
FreeRADIUS: FreeRADIUS Version: 1.1.7 or later (http://freeradius.org/download.html)
Yubico PAM Module: Yubico PAM Module Version 1.8 (https://developers.yubico.com/yubico-pam/)
Edit the radiusd configuration file “/etc/raddb/radiusd.conf” to make following changes:
* Change user and group to “root” to provide the root privileges to
radiusd daemon so that it can call and use pam modules for authentication.
NOTE: Generally, it is not a good security practice to assign root
privileges to a user for a daemon. However, since use of PAM requires root
privileges, this is a mandatory step here.
* In “authenticate” section uncomment pam to direct radiusd daemon to use PAM
module for authentication
Edit the client configuration file “/etc/raddb/clients.conf”
Add sample client for testing
Edit the user configuration file “/etc/raddb/users” to make following change:
Change "DEFAULT Auth-Type = System" to "DEFAULT Auth-Type = pam" for using PAM modules for user authentication
Build instructions for pam_yubico are available in the README. (https://developers.yubico.com/yubico-pam/)
Configuration instructions for pam_yubico are also available in the README. (https://developers.yubico.com/yubico-pam/)
Make sure you set your system up for either central authorization mapping, or user level mapping, as this will control which users can connect to the system using RADIUS.
Append the following line to the beginning of /etc/pam.d/radiusd file:
auth required pam_yubico.so id=16 debug authfile=/etc/yubikey_mappings
After the above configuration changes, whenever a user connects to the server using any RADIUS client, the PAM authentication interface will pass the control to Yubico PAM module.
The Yubico PAM module first checks the presence of authfile argument in PAM configuration. If authfile argument is present, it parses the corresponding mapping file and verifies the username with corresponding YubiKey PublicID as configured in the mapping file.
If valid, the Yubico PAM module extracts the OTP string and sends it to the Yubico authentication server or else it reports failure. If authfile argument is present but the mapping file is not present at the provided path PAM module reports failure. After successful verification of OTP Yubico PAM module from the Yubico authentication server, a success code is returned.
Although, user level configuration of pam_yubico is possible, this might not be a desired configuration option in case of radisud daemon in most enterprise.
Local effective selinux policy must be updated to provide sufficient privileges to radiusd daemon on system resources. Please follow the steps below to configure effective selinux policy for radiusd daemon:
Start the radiusd daemon
Test the RADIUS authentication with the test case provided in “Testing the configuration” section below
As radiusd daemon doesn’t have sufficient selinux privileges to access the system resources required for using pam modules, the RADIUS authentication will fail.
This will create the logs in either “/var/log/messages” or in “/var/log/audit/audit.log” depending on the selinux configuration.
We can use audit2allow utility to provide selinux privileges to radiusd by using following sequence of commands:
[root@testsrv ~]# audit2allow -m local -l -i /var/log/messages > local.te [root@testsrv ~]# checkmodule -M -m -o local.mod local.te [root@testsrv ~]# semodule_package -o local.pp -m local.mod [root@testsrv ~]# semodule -i local.pp
For more selinux policy updating information and explanation of above commands please visit the following website:
http://fedora.redhat.com/docs/selinux-faq-fc5/#id2961385
FreeRADIUS server first authorizes presence of user in the configured database and then authenticates it.
In a single factor YubiKey authentication, we must provide a PAM mechanism to authorize the presence of user.
We are using “pam_listfile.so” PAM module to provide a PAM mechanism to authorize the presence of user. For this, we need to provide a file containing authorized user names to the “pam_listfile.so” file. This file should contain user names with only one user name on each line as follows:
For example:
paul
The user_name file must be created/updated manually before configuration of Yubico PAM module for RADIUS authentication. Once this file is ready, we need to edit the FreeRADIUS PAM configuration file “/etc/pam.d/radiusd” and replace its contents with following lines:
auth sufficient pam_yubico.so id=16 debug authfile=/etc/yubikeyid account required pam_listfile.so onerr=fail item=user sense=allow file=<Absolute path of file containing user names>
Our test environment is as follows:
Operating System: Fedora release 8 (Werewolf)
FreeRADIUS Server : FreeRADIUS Version 1.1.7 and Version 2.1.3
Yubico PAM: pam_yubico Version 1.8
"/etc/pam.d/radiusd" file:
auth sufficient pam_yubico.so id=16 debug authfile=/etc/yubikeyid account required pam_listfile.so onerr=fail item=user sense=allow file=/etc/yubicousers
We have tested the pam_yubico configuration on following Linux sever platforms:
Fedora 8:
* Operating system: Fedora release 8 (Werewolf) * FreeRADIUS Server : FreeRADIUS Version 1.1.7 and Version 2.1.3 * Yubico PAM: pam_yubico Version 1.8
Fedora 6:
* Operating system: Fedora Core release 6 (Zod) * FreeRADIUS Server : FreeRADIUS Version 1.1.7 and Version 2.1.3 * Yubico PAM: pam_yubico Version 1.8
To test the RADIUS single factor authentication with YubiKey, we can use “radtest” radius client. The command is as follows:
[root@testsrv ~]# radtest {username} \
{password followed by YubiKey generated OTP} \
{radius-server}:{radius server port} \
{nas-port-number} \
{secret/ppphint/nasname}
[root@testsrv ~]# radtest test vrkvfefuitvfvgu...ildbdk 127.0.0.1 0 testing123
The FreeRADIUS server version 1.1.3 seems to have problems regarding memory management and it may result in Segmentation Fault if configured with Yubico PAM module. We recommend using FreeRADIUS server version 1.1.7 or above.