DEV Community


Posted on • Updated on

Active Directory LDAPS the easy way

Skip ahead to Setup LDAPS using self-signed cert made with openssl if you do not need any background information.
Also,check out my accompanying github repo which contains all the files used in this guide. Inside, see to quickly run through just the commands.

Insecure LDAP is dying, Long Live Secure LDAPS

Microsoft will begin enforcing secure connections for Active Directory LDAP in March of 2020. Update: Microsoft has extended the deadline to "second half of calendar year 2020". This is the third extension Microsoft has made since first announcing this change in 2017. Active Directory has long been a haven of questionable security. Microsoft has made several great improvements for security in recent years and this most recent change is designed to plug one of the long-lived security weaknesses of Active Directory.

Why is it needed

Many services using Active Directory communicate over plain-text LDAP binds on port 389 for authentication and queries. Active Directory joined machines authenticate using windows integrated authentication which uses encrypted methods such as kerberos or NTLM. In the same way that plain-text HTTP is insecure, LDAP is also vulnerable to man-in-the-middle attacks and the exposure of sensitive information such as username/passwords. LDAPS, like HTTPS, transmits its data over an encrypted tunnel using SSL or TLS.

How it works

For Active Directory to use LDAPS, just like a web server using HTTPS, it needs a certificate issued to it and installed. If you are familiar with certs for web servers then you are already familiar with the process. First, create a certificate signing request (CSR), send that to a certificate authority (CA), and then install the client certificate created from the CA. Here is a great article by cloudflare about SSL/TLS and certs.

Self-signed or public CA.

Publicly signed certs are often already trusted by many services, but are not free if the cert has a validity period of greater than a few months. For most systems connecting using LDAPS, this benefit of a cert from a public CA is moot since they have a separate truststore just for LDAPS that typically does not contain any public CAs. For a vast majority of people Self-signed is the way to go, since it is free and you can set long expiration dates.

Why not a Microsoft CA Server

When initially looking to configure LDAPS for AD I looked into creating a Microsoft CA server. I ran into several limitations for my use case. First, I found Microsoft's documentation to be quite long and unnecessarily confusing. Once I figured it all out, it was not too bad, but as you will see the openssl route is quite a bit easier as long as it fits your use case. The primary reason to use Microsoft CA Server is if you plan on issuing certs for other internal only services like internal web servers. Due to the abundance of methods to get free, publicly signed certs, like Let’s Encrypt for web servers, I prefer to use a publicly signed cert even for internal web servers.

See if your application is using plain-text LDAP

From the server running your application you can look at the outbound network traffic and check if there is anything communicating to one of your AD Domain Controllers IP addresses over the default LDAP port of 389. LDAPS uses port 636. The netstat command can be used on both linux and windows to see your open network connections.

Find connections on port 389: Linux

foo@bar:~$ netstat -antlp | grep 389 | grep ESTABLISHED
tcp        0      0        ESTABLISHED -
tcp        0      0       ESTABLISHED -
Enter fullscreen mode Exit fullscreen mode

We can see that this machine is communicating to port 389 on the ip which is an AD Domain controller in my test environment.

find connections on port 389: Windows

C:\Windows\system32>netstat -ant | findstr 389 | findstr ESTABLISHED
  TCP       ESTABLISHED     InHost
  TCP      ESTABLISHED     InHost
Enter fullscreen mode Exit fullscreen mode

Again we see which indicates a program connecting to a AD controller using LDAP on port 389

Setup LDAPS using self-signed cert made with openssl


  • openssl
  • Need to know:
    • your active directory domain name. ex:
    • your active directory domain controller's name. ex:

Here is how to install openssl if you do not already have it:

#For Debian/Ubuntu 
sudo apt-get install openssl
#For rhel/centos
sudo yum -y install openssl
Enter fullscreen mode Exit fullscreen mode

It is also possible to install it on windows. See this guide for installing openssl on windows:

Creating your own CA

First create a directory to work in. Pro tip: make your life easy and mount a directory on your AD controller from the machine with openssl. We will need to move a few files back and forth and mounting it over smb makes this easy. See these instructions on how to mount an smb share in Ubuntu

Create a text file named ca_san.conf with the following contents, modifying as needed. ex: "" to your domain.

[ req ]
distinguished_name = req_distinguished_name
req_extensions     = v3_ca

[ req_distinguished_name ]
# Descriptions
countryName=Country Name (2 letter code)
stateOrProvinceName=State or Province Name (full name)
localityName=Locality Name (eg, city)
0.organizationName=Your Company/Organization Name.
1.organizationName=Organizational Unit Name (Department)
commonName=Your Domain Name

#Modify for your details here or answer the prompts from openssl
0.organizationName_default=My Company Name LTD.
[ v3_ca ]
subjectAltName = @alt_names
#Modify for your details. Must include the commonName in the list below also. 
#The * will allow all Domain controllers with 
#the hostname to use the cert.
DNS.1 = *
DNS.2 =
Enter fullscreen mode Exit fullscreen mode

Next save that file to a directory named LDAPS, then run the following commands to create the CA key and cert:

foo@bar:~$ mkdir LDAPS && cd LDAPS

# generate the ca key, create a password and keep it for use throughout this guide.
foo@bar:~/LDAPS$ openssl genrsa -des3 -out ca.key 4096
Generating RSA private key, 4096 bit long modulus (2 primes)
Enter pass phrase for ca.key:
Verifying - Enter pass phrase for ca.key:

# create ca cert with valid of 10 years with info based off the 
# provided ca_san.conf file, it will prompt for the password we created earlier 
foo@bar:~/LDAPS$ openssl req -new -x509 \
    -extensions v3_ca \
    -days 3650 \
    -key ca.key \
    -out ca.crt \
    -config ca_san.conf

foo@bar:~/LDAPS$ ls
ca.crt  ca.key
Enter fullscreen mode Exit fullscreen mode

Now we have created two files: ca.key and ca.crt

Next, we will add the ca.crt as a Trusted Root Certificate and create a (CSR) on an AD controller

In powershell, as Admin, on an AD controller copy over the ca.crt file and run the following to import it as a Trusted Root Certificate:

#import the cert as a trusted CA on the domain controller
Import-Certificate -FilePath ca.crt  -CertStoreLocation 'Cert:\LocalMachine\Root' -Verbose
Enter fullscreen mode Exit fullscreen mode

Create a text file named request.inf with the following contents edited for your environment

;----------------- request.inf -----------------
 Signature="$Windows NT$"

;The Subject will need to be your active directory domain name
 Subject = ""
 KeySpec = 1
 KeyLength = 4096
 Exportable = TRUE
 MachineKeySet = TRUE
 PrivateKeyArchive = FALSE
 UserProtected = FALSE
 UseExistingKeySet = FALSE
 ProviderName = "Microsoft RSA SChannel Cryptographic Provider"
 ProviderType = 12
 RequestType = PKCS10
 KeyUsage = 0xa0

 OID = ; Server Authentication
;The following will add a subject alternative name of a wildcard cert on *
;so any ad controller with a hostname of can use it.
[Extensions] = "{text}"
_continue_ = "dns=*"
_continue_ = ""
Enter fullscreen mode Exit fullscreen mode

Next, on the AD controller run certreq passing in the request.inf we created and specifying the output file ad.csr

certreq -new request.inf ad.csr
Enter fullscreen mode Exit fullscreen mode

Copy the ad.csr over to your machine with openssl and create a new text file named v3ext.txt with the following contents, editing the alt_names to your domain:

# v3ext.txt
subjectAltName = @alt_names
#Modify for your details. Must include the commonName in the list below also. 
#The * will allow all Domain controllers with 
#the hostname to use the cert.
DNS.1 = *
DNS.2 =
Enter fullscreen mode Exit fullscreen mode

Now run the following command to generate the cert for AD:

# create ad_ldaps_cert by signing the csr
# 825 days is the maximum for a cert to be trusted as dictated by 
# the new 2019 guidelines from the CA/Browser Forum
# This is important since macOS has began to enforce this guideline
openssl x509 -req -days 825 \
    -in ad.csr \
    -CA ca.crt \
    -CAkey ca.key \
    -extfile v3ext.txt \
    -set_serial 01 \
    -out ad_ldaps_cert.crt
Enter fullscreen mode Exit fullscreen mode

Copy ad_ldaps_cert.crt over to the machine back to the AD Controller and accept the cert

# accept the signed cert 
certreq -accept ad_ldaps_cert.crt
Enter fullscreen mode Exit fullscreen mode

We can check that the cert has been imported by running the following powershell. We should see

PS C:\LDAPS> Get-ChildItem "Cert:\LocalMachine\My"

   PSParentPath: Microsoft.PowerShell.Security\Certificate::LocalMachine\My

Thumbprint                                Subject
----------                                -------
Enter fullscreen mode Exit fullscreen mode

Great, now our cert is imported and ready to be used. Now we can restart the AD Controller or create the following file and run a command to tell AD to start using LDAPS


changetype: modify
add: renewServerCertificate
renewServerCertificate: 1
Enter fullscreen mode Exit fullscreen mode

Then run this command passing in the text file:

PS C:\LDAPS> ldifde -i -f enable_ldaps.txt
Connecting to ""
Logging in as current user using SSPI
Importing directory from file "enable_ldaps.txt"
Loading entries..
1 entry modified successfully.

The command has completed successfully
Enter fullscreen mode Exit fullscreen mode

To test that we can use openssl to connect and verify, we can establish a secure connection to our AD controller

openssl s_client -connect -CAfile ca.crt
Enter fullscreen mode Exit fullscreen mode

Add Cert to all domain controllers.

To add the cert and privatekey to all of our domain controllers we need to export the cert/privatekey to a pfx file to be imported on each AD DC.

First, we need to get the Thumbprint of our cert to export it. Run this powershell to list your certs under the Cert:\LocalMachine\My cert store:

PS C:\LDAPS> Get-ChildItem "Cert:\LocalMachine\My"

   PSParentPath: Microsoft.PowerShell.Security\Certificate::LocalMachine\My

Thumbprint                                Subject
----------                                -------
Enter fullscreen mode Exit fullscreen mode

Specify a password and copy the thumbprint from the above output and replace it in the below command to export the cert/private key to a pfx file.

# For security reasons we must create a password to encrypt the privatekey. Edit for YOURPASSWORD
$pfxPass = (ConvertTo-SecureString -AsPlainText -Force -String "YOURPASSWORD")
#export cert/privatekey to a pfx file.
Get-ChildItem "Cert:\LocalMachine\My\087B0AB4E62DCE1D33323209EA81F2D58E0BF3B5" | Export-PfxCertificate -FilePath LDAPS_PRIVATEKEY.pfx -Password $pfxPass
Enter fullscreen mode Exit fullscreen mode

Now we will have a file named LDAPS_PRIVATEKEY.pfx that contains the cert and privatekey for our active directory domain controllers to use.

Test all the Domain Controllers

The Following Powershell will test all of our Active Directory Domain Controllers for LDAPS:

$AllDCs = Get-ADDomainController -Filter * -Server | Select-Object Hostname
 foreach ($dc in $AllDCs) {
    $LDAPS = [ADSI]"LDAP://$($dc.hostname):636"
    #write-host $LDAPS
    try {
    $Connection = [adsi]($LDAPS)
    } Catch {
    If ($Connection.Path) {
    Write-Host "Active Directory server correctly configured for SSL, test connection to $($LDAPS.Path) completed."
    } Else {
    Write-Host "Active Directory server not configured for SSL, test connection to LDAP://$($dc.hostname):636 did not work."
Enter fullscreen mode Exit fullscreen mode


You now have all your domain controllers configured to use Secure LDAPS. But this is just half the battle, we now need to configure all of our Services, Apps, AD joined macOS computers and Servers to use LDAPS.

How to find what systems and servers are using insecure LDAP Binds

Read my next article to learn how to turn on logging in Active Directory and export the logs to CSV using powershell.
Coming soon.

Top comments (8)

ema07cqc profile image

Hello, thanks for this Step to Step guide.

In my case, I have 3 DCs (2008R2 and 2016) + 400 endpoints (Windows 8.1 and Windows 10 1709 or later).

If I setup Secure LDAPS following this guide... those endpoints would be able to connect normally?

and what about all the services that today are connecting through 389?

Thank you!! Have a nice week.

bondr007 profile image

Hi Emanuel,

The communication between Active Directory and client machines is secured using a different protocol called kerberos for authentication. Domain joined machines such as your windows endpoints on windows 8.1 and 10 should not be effected since their traffic for authentication does not use LDAP or LDAPS, instead is uses a proprietary implementation of kerberos on port 88. LDAP and LDAPS are primarily used servers such as a web server that user Active Directory to authenticate users, or some client applications that query active directory. Some other examples are linux machines used with Active Directory can use LDAP(S), (there is also ways to use kerberos on linux domain joined machines), Mac OS uses LDAP(S) for authentication when joined to an active directory domain. When you enable LDAPS, LDAP 389 traffic does not go away. Microsoft has indefinitely extended the deadline. The March 2020 update did add the ability to enforce secure channel binding in LDAP: I have not had the opportunity to test this yet.

ema07cqc profile image

Hi there! First of all, thank you so much for your time and dedication to answer my question. Very clear! I did not know that workstations used Kerberos... So I'm going to go through those steps. Thank you very much again and have a good week!!!


ema07cqc profile image

Hi there. Hope you are doing well and safe.
I followed your tutorial 20 days ago and everything is working well (Windows Workstations i.e).
The connection from a linux to the main server is OK, using:
openssl s_client -connect srv-ad-01.mydomain.local:636 -CAfile ca.crt

but its not working when trying to connect the other 3 DCs (where I imported pfx). Im getting this error:

no peer certificate available
No client certificate CA names sent
SSL handshake has read 0 bytes and written 0 bytes
New, (NONE), Cipher is (NONE)

I followed this guide to import the PFX file:
How to Install Certificates on Microsoft Active Directory LDAP 2012

There is another way to import that pfx file?

Thanks again.

Thread Thread
bondr007 profile image

Hi Emanuel,

Sorry it took so long to reply.

You can export the cert/privatekey and import them on the rest of your domain controllers using the commands listed here to do this:

daileng profile image
Dailen Gunter

I've encountered some issues with importing the commands. I found an article regarding common causes but only found one issue. So I made local security policy change to enable using a private key without strong encryption, the problem still occurs.

Connecting to "[redacted]"

Logging in as current user using SSPI

Importing directory from file "c:\temp\ldaps\enable_ldaps.txt"

Loading entries
1: (null)
Entry DN: (null)
changetype: modify
Attribute 0) renewServerCertificate:1

Add error on entry starting on line 1: Inappropriate Authentication

The server side error is: 0x8009030e No credentials are available in the security package

The extended server error is:
8009030E: SecErr: DSID-0C0203F5, problem 4001 (INAPPROPRIATE_AUTH), data 0

0 entries modified successfully.

An error has occurred in the program

glenn_rieger_08b7787c5f34 profile image
Glenn Rieger

This a great guide and works well but how does one renew the cert when it expires? Because it's a PKCS10 cert, you can't just add the renewal line (and existing cert hash) into the request.inf file. I know this is an old article but hopefully someone will see this and point me in the right direction.


domeo profile image

Great guide!

I'm trying to install a wildcard certificate issued by Sertigo through OpenSSL installed on Windows Server. Do you have any experience or tips for this?