A lot of appliances and/or security solutions use LDAP to synchronize users from an Active Directory or an eDirectory environment. Active Directory is LDAP enabled by default. If you would like to harden your network, you would like to use LDAPS.
LDAPS is a term to refer to LDAP communication over SSL. Intercepted LDAPS traffic cannot be read easily by hackers. In an Active Directory environment you need to have at least one Certificate Authority (CA) to enable LDAPS. Windows uses Server Authentication certificates for the LDAPS operations.
Last week I had a customer complaining that people weren’t able to access their webmail via a Microsoft ISA reverse proxy. The cause of the problem was an expired Server Certificate on the specific domain controller. The reverse proxy server uses LDAPS to authenticate the user against an Active Directory. The following event log was found on the reverse proxy server.
To resolve the problem I had to renew the Server Authentication certificate on the domain controller. I decided to use the “Windows method” by using the Windows CA to renew the certificate. From the domain controller with the expired certificate I opened IE and enter the URL:
http://<IP address CA>/certsrv
This opens the Microsoft Certificate Services webpage of the CA. The following screenshots show the request and installation procedure for the certificate renewal.
Normally I use OpenSSL to generate the certificate signing request, which is submitted to the CA. In that scenario I had to choose option 2. This time I decide to generate the csr via the webpage and choose the first option: Create and submit a request to this CA.
The csr is generated with the information from the screenshot above. Because I had to renew a Server Authentication certificate, I choose the Web Server certificate template. The Name field is very important and should match the FQDN of the LDAPS server. It is also important to select the Store certificate in local computer certificate store option. This ensures that the certificate isn’t installed in the user’s certificate store, because the certificate cannot be exported with private key.
When you submit the certificate request, you have to wait until the request is approved. The approval has to be done by someone who manages the CA environment. If you open the CA MMC snap-in you will see one or more pending request. The pending request needs to be approved. After the request was approved, I browsed to the Microsoft Certificate Services webpage, like shown below.
I choose the option View the status of a pending certificate request. Remember that I did the whole procedure on the LDAPS server to be sure that the certificate is stored in the servers local computer certificate store. The last step involves installing the certificate in the local computers certificate store. After the installation I always check the store to see if the private key is present for the certificate.
The renewal of the certificate is almost done. The LDAPS services depends on the process LSASS.exe. To “associate” the SSL certificate with the LDAPS server I needed to reboot the server. During the reboot the first valid Server Authentication SSL certificate within the local computer certificate store is used by the LDAPS server.
The reverse proxy server was able to use LDAPS again after the reboot of the specific domain controller.