Network security: LDAP client signing requirements


Applies To: Windows Server 2003, Windows Vista, Windows XP, Windows Server 2008, Windows 7, Windows 8.1, Windows Server 2008 R2, Windows Server 2012 R2, Windows Server 2012, Windows 8

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.


This policy setting determines the level of data signing that is requested on behalf of client computers 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.


This policy setting does not have any impact on ldap_simple_bind or ldap_simple_bind_s. LDAP client computers that are running Windows XP Professional or Windows Vista do not use ldap_simple_bind or ldap_simple_bind_s to communicate with a domain controller.

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

  1. Set Domain controller: LDAP server signing requirements to Require signature. If you set the server to require LDAP signatures, you must also set the client computers to do so. Not setting the client computers will prevent client computers from communicating with the server. This can cause many features to fail, including user authentication, Group Policy, and logon scripts.


GPO_name\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

Operating system version differences

There are no differences in this policy between operating systems beginning with Windows Server 2008.

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 computer restart when they are saved locally or distributed through Group Policy.

Group Policy

Modifying this setting may affect compatibility with client computers, 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.


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.


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

Potential impact

If you configure the server to require LDAP signatures, you must also configure the client computers. If you do not configure the client computers, they cannot communicate with the server, which could cause many features to fail, including user authentication, Group Policy, and logon scripts.