LDAP Channel Binding and LDAP Signing Requirements – March update default behavior

Hi All, Alan here again, this time trying to give some details on these two settings that will become active from March 2020 and they are creating some misunderstandings.

Let's start saying that since Windows Server 2008 we have events 2886,2887,2888 and 2889 logged every 24 hours on the Directory Services log that tells us we are using these unsecure protocols

This information is preliminary and is subject to revision.This article is a living document, written over time and is subject to change. When guidance presented in this article is in direct conflict with official documentation, one must defer to official documentation.



Telling us that our DCs are not requiring LDAP signing


2887 (already on by default and logged every 24 hours)

Telling us how many such binds occurred


The suggested path to resolve this error is do modify the registry of the DC to allow it log those failures.

Registry to add:

Reg Add HKLMSYSTEMCurrentControlSetServicesNTDSDiagnostics /v “16 LDAP Interface Events” /t REG_DWORD /d 2


Once the registry key “16 LDAP Interface Events” is configured we will have event 2889 telling us who is using this type of unsecure protocol


This is the Event ID you want to check in order to understand which IP Address and Accounts are making these requests.

Once you open Event 2889 in Details you will have

Client IP address: “Value”
Identity the client attempted to authenticate as: “Value”


If the directory server is configured to reject unsigned SASL LDAP binds or LDAP simple binds over a non-/ connection, the directory server will log a summary event 2888 one time every 24 hours when such bind attempts occur.


Please refer to official article for new updated information.

New information on these settings will soon be published

The March 2020 3B updates consist of the following on both new and existing domain controllers:

  • New audit events
  • Additional logging 
  • A remapping of values

The March 2020 3B updates specifically DO NOT:

Make any changes to the current LDAP signing or channel binding settings, default or otherwise, that apply to new or existing domain controllers.

AUDITING LDAP Channel Binding : 

Logging of LDAP Binds Not Using CBT

NOTE: these events will only be logged once the update is installed

Same registry key as for LDAP Signing, so “16 LDAP Interface Events = 2 ”

EventID 3039 Informational

EventID 3040 Informational


Very important NOTE: You need to have this CVE-2017-8563 installed on your clients as a prerequisite before enabling LDAP Channel Binding and LDAP Integrity on DCs

ADV190023 | Microsoft Guidance for Enabling LDAP Channel Binding and LDAP Signinghttps://portal.msrc.microsoft.com/en-us/security-guidance/advisory/ADV190023

CVE-2017-8563 | Windows Elevation of Privilege Vulnerability (REQUIRED)

An elevation of privilege vulnerability exists in Microsoft Windows when a man-in-the-middle attacker is able to successfully forward an request to a Windows LDAP server, such as a system running Active Directory Domain Services (AD DS) or Active Directory Lightweight Directory Services (AD LDS), which has been configured to require signing or sealing on incoming connections.

The update addresses this vulnerability by incorporating support for Extended Protection for security feature, which allows the LDAP server to detect and block such forwarded requests once enabled.

Main thing to point out is which values will these settings have once the March 2020 update rolls out.

Here they are:

  • LDAP Channel Binding = 1 (after update)

AD – HKEY_LOCAL_MACHINESystemCurrentControlSetServicesNTDSParameters

ADLDS – HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesParameters

value:1 indicates enabled, when supported. All clients that are running on a version of Windows that has been updated to support channel binding tokens (CBT) must provide channel binding information to the server. Clients that are running a version of Windows that has not been updated to support CBT do not have to do so. This is an intermediate option that allows for application compatibility.

Important Notes 

– Before you enable this setting on a Domain Controller, clients must install the security update that is described in CVE-2017-8563. Otherwise, compatibility issues may arise, and LDAP authentication requests over SSL/ that previously worked may no longer work. By default, this setting is disabled.

– The LdapEnforceChannelBindings registry entry must be explicitly created.

– LDAP server responds dynamically to changes to this registry entry. Therefore, you do not have to restart the computer after you apply the registry change.

LDAP Channel Binding: To maximize compatibility with older operating system versions (Windows Server 2008 and earlier versions), we recommend that you enable this setting with a value of 1
To explicitly disable the setting, set the LdapEnforceChannelBinding entry to 0 (zero).

Windows Server 2008 and older systems require that Microsoft Security Advisory 973811, available in “KB 968389 Extended Protection for Authentication”, be installed before installing CVE-2017-8563. 

If you install CVE-2017-8563 without KB 968389 on a Domain controller or AD LDS instance, all LDAPS connections will fail with LDAP error 81 – LDAP_SERVER_DOWN. In addition, we strongly recommended that you also review and install the fixes documented in the Known Issues section of KB 968389.


  • LDAP Server Integrity (signing) = enabled by default (after update)


I want to note that this article shows two sections related to server and client, that need to be configured:

set the server LDAP signing requirement nbsp;nbsp;

– How to set the client LDAP signing requirement through a domain Object nbsp;nbsp;


LDAP Signing – No Downtime

After installing ADV190023 both settings (Legacy and Not Defined) will enforce Require Signature

Only None = 0 (OFF) will not enforce Require Signature

NOTE (not recommended, but if you really want to stick with disabling):

This means that value of “0” in registry means “OFF” and this also means that the update will not change the setting and not enforce Require Signing

DC: HKLMSYSTEMCurrentControlSetServicesNTDSParameters  –> LDAPServerIntegrity = 0

LDAP Signing Group Policy – Behavior Change Example


If we don't want to wait for the March 2020 update

  1. Enable LdapEnforceChannelBinding = 1  (must have CVE-2017-8563)
  2. Enable LDAP Server Signing 
    • DCs = policy “Domain controller: LDAP server signing requirements” = Require Signing
    • Servers/Clients = policy “Network security: LDAP client signing requirements = Require Signing


Summarizing a little this long article we can state the following:

  1. Directory Services Log is our friend: Event IDs 2886,2887,2888,2889
  2. On Clients we need to have as a prerequisite CVE-2017-8563 “Extended Protection for Authentication” before we enable LDAP CBT and LDAP Signing
  3. DCs –> Enable LDAP Signing and LDAP CBT

Hope this helps understanding how these settings work and how they will be configured after the March 2020 update, which can affect your LDAP Authentication if you don't make any changes.

Regards to All

Alan @ PFE


This article was originally published by Microsoft's Azure Blog. You can find the original article here.