Chapter 4. Configuring SSSD to use LDAP and require TLS authentication
The System Security Services Daemon (SSSD) is a daemon that manages identity data retrieval and authentication on a Red Hat Enterprise Linux host. A system administrator can configure the host to use a standalone LDAP server as the user account database. The administrator can also specify the requirement that the connection with the LDAP server must be encrypted with a TLS certificate.
The SSSD configuration option to enforce TLS,
ldap_id_use_start_tls, defaults to
false. When using
ldap:// without TLS for identity lookups, it can pose a risk for an attack vector, namely a man-in-the-middle (MITM) attack which could allow you to impersonate a user by altering, for example, the UID or GID of an object returned in an LDAP search.
Ensure that your setup operates in a trusted environment and decide if it is safe to use unencrypted communication for
id_provider = ldap. Note
id_provider = ad and
id_provider = ipa are not affected as they use encrypted connections protected by SASL and GSSAPI.
If it is not safe to use unencrypted communication, you should enforce TLS by setting the
ldap_id_use_start_tls option to
true in the
4.1. An OpenLDAP client using SSSD to retrieve data from LDAP in an encrypted way
The authentication method of the LDAP objects can be either a Kerberos password or an LDAP password. Note that the questions of authentication and authorization of the LDAP objects are not addressed here.
Configuring SSSD with LDAP is a complex procedure requiring a high level of expertise in SSSD and LDAP. Consider using an integrated and automated solution such as Active Directory or Red Hat Identity Management (IdM) instead. For details about IdM, see Planning Identity Management.
4.2. Configuring SSSD to use LDAP and require TLS authentication
Complete this procedure to configure your Red Hat Enterprise Linux (RHEL) system as an OpenLDAP client.
Use the following client configuration:
- The RHEL system authenticates users stored in an OpenLDAP user account database.
- The RHEL system uses the System Security Services Daemon (SSSD) service to retrieve user data.
- The RHEL system communicates with the OpenLDAP server over a TLS-encrypted connection.
You can alternatively use this procedure to configure your RHEL system as a client of a Red Hat Directory Server.
- The OpenLDAP server is installed and configured with user information.
- You have root permissions on the host you are configuring as the LDAP client.
On the host you are configuring as the LDAP client, the
/etc/sssd/sssd.conffile has been created and configured to specify
You have a PEM-formatted copy of the root CA signing certificate chain from the Certificate Authority that issued the OpenLDAP server certificate, stored in a local file named
Install the requisite packages:
# dnf -y install openldap-clients sssd sssd-ldap oddjob-mkhomedir
Switch the authentication provider to
# authselect select sssd with-mkhomedir
core-dirsrv.ca.pemfile containing the root CA signing certificate chain from the Certificate Authority that issued the OpenLDAP server’s SSL/TLS certificate into the
# cp core-dirsrv.ca.pem /etc/openldap/certs
Add the URL and suffix of your LDAP server to the
URI ldap://ldap-server.example.com/ BASE dc=example,dc=com
/etc/openldap/ldap.conffile, add a line pointing the TLS_CACERT parameter to
# When no CA certificates are specified the Shared System Certificates # are in use. In order to have these available along with the ones specified # by TLS_CACERTDIR one has to include them explicitly: TLS_CACERT /etc/openldap/certs/core-dirsrv.ca.pem
/etc/sssd/sssd.conffile, add your environment values to the
ldap_search_baseparameters and set the
[domain/default] id_provider = ldap autofs_provider = ldap auth_provider = ldap chpass_provider = ldap ldap_uri = ldap://ldap-server.example.com/ ldap_search_base = dc=example,dc=com ldap_id_use_start_tls = True cache_credentials = True ldap_tls_cacertdir = /etc/openldap/certs ldap_tls_reqcert = allow [sssd] services = nss, pam, autofs domains = default [nss] homedir_substring = /home …
/etc/sssd/sssd.conf, specify the TLS authentication requirement by modifying the
ldap_tls_reqcertvalues in the
… cache_credentials = True ldap_tls_cacert = /etc/openldap/certs/core-dirsrv.ca.pem ldap_tls_reqcert = hard …
Change the permissions on the
# chmod 600 /etc/sssd/sssd.conf
Restart and enable the SSSD service and the
# systemctl restart sssd oddjobd # systemctl enable sssd oddjobd
(Optional) If your LDAP server uses the deprecated TLS 1.0 or TLS 1.1 protocols, switch the system-wide cryptographic policy on the client system to the LEGACY level to allow RHEL to communicate using these protocols:
# update-crypto-policies --set LEGACY
For more details, see the Strong crypto defaults in RHEL 8 and deprecation of weak crypto algorithms Knowledgebase article on the Red Hat Customer Portal and the
Verify you can retrieve user data from your LDAP server by using the
idcommand and specifying an LDAP user:
# id ldap_user uid=17388(ldap_user) gid=45367(sysadmins) groups=45367(sysadmins),25395(engineers),10(wheel),1202200000(admins)
The system administrator can now query users from LDAP using the
id command. The command returns a correct user ID and group membership.