Active Directory

My Very Own CA, How Sweet :)

Just splurging this down here for next time, as I had to go trawling for this info in various old text files today… Very related to https://blog.oholics.net/creating-simple-ssl-certificates-for-server-authentication-using-openssl/, but using my own CA rather than an enterprise or public CA.

I was working in my lab today to setup SLDAP on my lab domain controller. I was doing this to validate the syntax of ldapsearcher, on a Ubuntu machine, in different cases and also to see if I could determine the reason I was seeing a particular error (see https://blog.oholics.net/ldapsearch-syntax-for-simple-ldap-and-sldap/).

I want to KISS (keep things simple stupid), so was going to use the rootCA that I setup with OpenSSL a few years ago (running on my Windows machine).

Back then I ran the following commands to create the “top level” Root CA certificate and Private Key:

openssl genrsa -out rootCA.key 2048
openssl req -x509 -new -nodes -key rootCA.key -sha256 -days 1024 -out rootCA.pem

To generate my domain controller certificate today, I used (with an edited openssl.conf file of course):

openssl genrsa -out dc.oholics.net.key 2048
openssl req -new -key dc.oholics.net.key -out dc.oholics.net.csr
openssl x509 -req -in dc.oholics.net.csr -CA rootCA.pem -CAkey rootCA.key -CAcreateserial -out dc.oholics.net.crt -days 500 -sha256
openssl pkcs12 -export -out dc.oholics.net.pfx -inkey dc.oholics.net.key -in dc.oholics.net.crt -certfile dc.oholics.net.crt

On the domain controller, I installed the dc.oholics.net.pfx file into the computer personal store and the rootCA.pem into the computer trusted root certification authorities store. Reboot and done..

Ldapsearch Syntax for Simple LDAP and SLDAP

Another case of “I’ve done this before, but never wrote it down”, so revisiting this took far longer than it should have. But now it is here, that won’t happen again.. right?? I’ll probably never need it again now… typical..

OK, so a straight forward non-secure ldapsearch command, obtains everything (-h can be IP or FQDN):

ldapsearch -h 192.168.1.201 -p 389 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>”

A secure ldapsearch command, using TLS on port 389, obtains everything (Note the use of the -Z switch and the use of FQDN):

ldapsearch -h dc.oholics.net -p 389 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>” -Z

A secure ldapsearch command, using SSL on port 636, obtains everything (note the use of -H and the LDAP Uniform Resource Identifier):

ldapsearch -H ldaps://dc.oholics.net:636 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>”

These commands all work just fine. Just for fun, make the last query type find something in particular – Look for a user account by its DN:

ldapsearch -H ldaps://dc.oholics.net:636 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>” “(&(objectclass=User)(distinguishedName=CN=John E Smoke,OU=Users,DC=oholics,DC=net))”

Now for some errors!

For both TLS and SSL on port 636, using the IP as the host (-h or -H) fails. It MUST use the FQDN of the target system. Why? because the certificate on the DC only refers to the FQDN of the server.

SSL/ 636 – The error “Can’t contact LDAP server (-1)” was really stumping me as there is little to go on in the error message. Doing a network capture, just shows the handshake start, but the DC ultimately just says “Go Away!”. It resets the connection attempt.

A few things learnt:

1. Using -h FQDN and -p 636 results in Can’t contact LDAP server (-1) (the URI method above must be used)

ldapsearch -h dc.oholics.net -p 636 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>”
ldap_sasl_bind(SIMPLE): Can’t contact LDAP server (-1)

2. Using -h IP Address and -p 636 results in Can’t contact LDAP server (-1)

ldapsearch -h 192.168.1.201 -p 636 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>”
ldap_sasl_bind(SIMPLE): Can’t contact LDAP server (-1)

3. Using -H with IP Address in URI and -p 636 results in Can’t contact LDAP server (-1)

ldapsearch -H ldaps://192.168.1.201:636 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>”
ldap_sasl_bind(SIMPLE): Can’t contact LDAP server (-1)

Additionally, for TLS connection. Using the IP address of the DC, resulted in a different, but much more helpful error message:

ldapsearch -h 192.168.1.201 -p 389 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>” -Z
ldap_start_tls: Connect error (-11)
additional info: TLS: hostname does not match CN in peer certificate

Also, where a Domain Controller has the setting “Domain controller: LDAP server signing requirements” set to Require signing. When trying to initiate an insecure LDAP query with ldapsearch, it fails as follows:

ldapsearch -h 192.168.1.201 -p 389 -b “DC=oholics,DC=net” -D “CN=svc-LDAPBind,OU=ServiceAccounts,DC=oholics,DC=net” -w “<MyPass>”
ldap_bind: Strong(er) authentication required (8)
additional info: 00002028: LdapErr: DSID-0C090257, comment: The server requires binds to turn on integrity checking if SSL\TLS are not already active on the connection, data 0, v2580

Well that was a fun day 🙂

Backup and Clear Domain Controller Security Event Logs

A post related to https://blog.oholics.net/logparser-loves-security-logs/, for Case 3.

If you don’t manage security logs by regularly backing them up and clearing them, you risk losing important historical information. Additionally, running a LogParser query against a large, unmanaged security event log takes a long time.

The below script is designed to be run daily at the end of the day to backup the security event log on a Domain Controller and then clear its contents. Additionally, the logs are archived off to two windows shares to allow for long term storage.

The script makes use of Jaap Brasser’s DeleteOld script (https://gallery.technet.microsoft.com/scriptcenter/Delete-files-older-than-x-13b29c09) to carry out tidy up operations of the local staging folder. In practice, I used the same script to manage the archive folders too, keeping 365 days worth of logs.

Usage: .\BACKUP_AND_CLEAR_EVENTLOGS.ps1 <DomainController> $clear

Make sure that the security event log maximum size is increased to a high enough level to ensure that none of the days logs get overwritten. Judging that size will depend on the number of events per day or alternatively just set to “do not overwrite events”.

Note: the event ID’s are purely made up 😉

Can’t rename, move or delete an OU

Today, I came across something that had me quite stumped…. well for a few minutes anyway 🙂

I was doing some tidying up of a domain, I found an OU that was incorrectly named, it was not to design. I thought, I’ll just rename it, but found that the option to do so was not available.

I took a look at the attributes of the OU, two immediately struck me as odd:

systemFlags was set to DISALLOW_DELETE|DOMAIN_DISALLOW_RENAME|DOMAIN_DISALLOW_MOVE

 

 

 

 

 

 

 

 

 

isCriticalSystemObject was set to TRUE:

 

 

 

 

 

 

 

 

 

Neither of these attributes could be modified, an error was thrown if attempted.

The simple answer: This OU had been set as the default location for new computer objects via redircmp 

By running redircmp CN=Computers,DC=oholics,DC=net (or your other true destination):

  • The systemFlags attribute was banished
  • The isCriticalSystemObject attribute was set to FALSE
  • The OU could be renamed, moved and deleted 😉