Securing LDAP

LDAP is vulnerable to various security threats, including spoofing of directory services, attacks against the databases that provide the directory services. This isn't to say that LDAP is completely vulnerable. LDAP supports a number of different security mechanisms, beginning from when clients initially connect to an LDAP server.

LDAP clients must authenticate to the server before being allowed access to the directory. Clients (users, computers, or applications) connect to the LDAP server using a distinguished name and authentication credentials (usually a password). Authentication information is sent from the client to the server as part of a "bind" operation, and the connection is later closed using an "unbind" operation. Unfortunately, it is possible for users to make the connection with limited or no authentication, by using either anonymous or simple authentication. LDAP allows for anonymous clients to send LDAP requests to the server without first performing the bind operation. While anonymous connections don't require a password, simple authentication will send a person's password over the network unencrypted.To secure LDAP, anonymous clients should be limited or not used, ensuring that only those with proper credentials are allowed access to the information. Optionally, the connection can use TLS to secure the connection, and protect any data transmitted between the client and server.

LDAP can also be used over SSL, which extends security into the Internet. LDAPS is Secure LDAP, which encrypts LDAP connections by using SSL or TLS. Some of these types of services integrate as objects, such as PKI certificates, in the authentication process using Smart Card technologies, and in the extended properties of account objects so that they can support extra security requirements. To use SSL with LDAP, the LDAP server must have an X.509 server certificate. Additionally, SSL/TLS must be enabled on the server.

Another issue that can impact the security of LDAP is packet sniffing. As we discussed earlier in this tutorial, packet sniffers are software that can capture packets of data from a network, and allow a person to view its contents. If the information traveling over LDAP is unencrypted, the packets of data could be captured, and analysis of the packets could provide considerable information about the network. In addition to using encryption, ports can be blocked to prevent access from the Internet. LDAP uses TCP/UDP port 389 and LDAPS uses port 636. By blocking these ports from the Internet, it will prevent those outside of the internal network from listening or making connections to these ports.

The challenge with using a protocol such as LDAP is that the connectivity must be facilitated through a script or program.These types of scripts must indicate the location of the objects within the directory service to access them. If the administrator wants to write a quick, simple script, this means that the name of the directory service and the names and locations of the objects that are being accessed must each be placed in the script and known prior to the script being written. If they need to access a different object, they usually need to rewrite the script or develop a much more complex program to integrate the directory services. Even so, compare scripting to native access with queries and interactive responses, and the value of a homogenous network with a single directory service is revealed. In a homogenous network, there is no need to logically connect two directory services with a script.This greatly reduces the time and effort involved in administering the network. Homogenous networks are unusual at best.With multiple types of network OSes, desktop OSes, and infrastructure OSes available today, it is likely that there will be multiple systems around. It follows that they all must be managed in different ways.

LDAP-enabled Web servers can handle authentication centrally, using the LDAP directory.This means users will only need a single login name and password for accessing all resources that use the directory. Users benefit from single sign-on to allow access to any Web server using the directory, or any password-protected Web page or site that uses the directory.The LDAP server constitutes a security realm, which is used to authenticate users.

Another advantage of LDAP security for Web-based services is that access control can be enforced based on rules that are defined in the LDAP directory instead of the administrator having to individually configure the OS on each Web server.

There are security programs available, such as PortalXpert Security, which can be used with LDAP to extend enforcement of the security policies that are defined by the LDAP directory to Web servers that are not LDAP enabled, and provide role-based management of access controls.

NOTE For more detailed information about LDAP security issues, see the white paper titled "Introduction to Security of LDAP Directory Services" by Wenling Bao at the SANS Institute Web site at http://rr.sans.org/dir/LDAP.php.