Network security: LDAP client signing requirements

Applies to

  • Windows 10

This security policy reference topic for the IT professional describes the best practices, location, values, policy management and security considerations for this policy setting. This information applies to computers running at least the Windows Server 2008 operating system.

Reference

This policy setting determines the level of data signing that is requested on behalf of client devices that issue LDAP BIND requests. The levels of data signing are described in the following list:

  • None. The LDAP BIND request is issued with the caller-specified options.
  • Negotiate signing. If Transport Layer Security/Secure Sockets Layer (TLS/SSL) has not been started, the LDAP BIND request is initiated with the LDAP data signing option set in addition to the caller-specified options. If TLS/SSL has been started, the LDAP BIND request is initiated with the caller-specified options.
  • Require signing. This level is the same as Negotiate signing. However, if the LDAP server's intermediate saslBindInProgress response does not indicate that LDAP traffic signing is required, the caller is returned a message that the LDAP BIND command request failed.

Misuse of this policy setting is a common error that can cause data loss or problems with data access or security.

Possible values

  • None
  • Negotiate signing
  • Require signature
  • Not Defined

Best practices

  • Set both the Network security: LDAP client signing requirements and Domain controller: LDAP server signing requirements settings to Require signing. To avoid usage of unsigned traffic, set both client and server sides to require signing. Not setting one of the sides will prevent client computers from communicating with the server. This can cause many features to fail, including user authentication, Group Policy, and logon scripts.

Location

Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options

Default values

The following table lists the actual and effective default values for this policy. Default values are also listed on the policy’s property page.

Server type or GPO Default value
Default Domain Policy Not defined
Default Domain Controller Policy Not defined
Stand-Alone Server Default Settings Negotiate signing
DC Effective Default Settings Negotiate signing
Member Server Effective Default Settings Negotiate signing
Client Computer Effective Default Settings Negotiate signing

Policy management

This section describes features and tools that are available to help you manage this policy.

Restart requirement

None. Changes to this policy become effective without a device restart when they are saved locally or distributed through Group Policy.

Group Policy

Modifying this setting may affect compatibility with client devices, services, and applications.

Security considerations

This section describes how an attacker might exploit a feature or its configuration, how to implement the countermeasure, and the possible negative consequences of countermeasure implementation.

Vulnerability

Unsigned network traffic is susceptible to man-in-the-middle attacks in which an intruder captures the packets between the client computer and server, modifies them, and then forwards them to the server. For an LDAP server, this susceptibility means that an attacker could cause a server to make decisions that are based on false or altered data from the LDAP queries. To lower this risk in your network, you can implement strong physical security measures to protect the network infrastructure. Also, you can make all types of man-in-the-middle attacks extremely difficult if you require digital signatures on all network packets by means of IPsec authentication headers.

Countermeasure

Configure the Network security: LDAP client signing requirements setting to Require signing.

Potential impact

If you configure the client to require LDAP signatures, it may fail to communicate with the LDAP servers that do not require requests to be signed. To avoid this issue, make sure that both the Network security: LDAP client signing requirements and Domain controller: LDAP server signing requirements settings are set to Require signing.