Certificate Services and Domain Controllers

When you create a new instance of an Enterprise Certificate server in the forest, you'll find that with a vanilla installation all of your domain controllers start to register certificates based on the Domain Controllers v1 template. This can be troublesome if you already have certificates in the local computer stores on DCs because the DCs may suddenly switch to use these new ones.
This will happen despite the fact that there are no auto-enrollment GPOs in place.

The reason for this is that it is just hard-coded into the operating system for DCs to auto-enroll using the Domain Controller certificate template, regardless of the presence of any policies instructing them to do this.
If there were a policy in place then you would likely find that the DCs would auto-enroll a Domain Controller  Authentication certificate instead as this supersedes the Domain Controller one.

To prevent it, remove that certificate template from the CA.
This can be done by either deleting it from the Certificate Templates container through the Certification Authority snap-in, or by configuring LoadDefaultTemplates=False (or LoadDefaultTemplates=0) in the CAPolicy.inf file so that the default v1 templates are never loaded on to the CA at installation time.
This is my preferred way as I never use the v1 templates (the general practice is to create your own templates). The v1 templates also cannot be auto-enrolled as this permission does not exist on a v1 template.

Creating iSCSI Volumes on Windows clusters

I created this to remind me of all of the steps that need to be done in order to create an iSCSI volume that can be shared across multiple servers (under the assumption that these servers will be clustered).

On the server that will host the shared volume, install Microsoft iSCSI Software Target. This can be dowloaded for free. It will bring up a web page that allows you to install the software. The installation will work out what version of the OS you are running and install the correct software.

Once installed:

1. Launch Microsoft iSCSI Software Target.
2. Right click Devices and Create Virtual Hard Disk.
3. Under File, put in the path to the virtual hard disk and call it whatever you want with a .vhd extension.
4. Put in the size of the volume that you want to create. The description can be whatever you want.
5. There won't be any iSCSI targets yet so just click next on this screen and finish.
6. Then, under iSCSI Targets, this is where we configure who can connect to the disk.
7. Right click - Create iSCSI Target.
8. iSCSI Initiator Identifers - Advanced - Add - specify the IP addresses (or whatever) of the clients that will be connecting. Here, if you are having multiple servers connecting to it, add both IP addresses. Accept the warning and click Finish.
9. Click on the disk that was created under Devices and right click - Assign/Remove Target.
10. Add the iSCSI target that was just created.
11. Next, swap to the client machines that need to connect to the iSCSI volume.
12. In Administrative Tools, launch iSCSI Initiator. It will want to start the service so accept this.
13. In the target field, type the IP address of the machine hosting the iSCSI volume and then Quick Connect - Done. If you are using a separate NIC to make the iSCSI connection, you could find that this stage fails. In my case, the additional NIC was just for this iSCSI connection, and I wasn't publishing this NIC to DNS and hadn't configured DNS servers for it. In order to get it to work I had to disable the production interface first before this step would work.
14. Once working it should show the name of the iSCSI target name as part of the name of the discovered target e.g. iqn.1991-05.com.microsoft:-iSCSITargetName>-target.
15. The Discovery tab will show the targets - no need to do anything on this screen.
16. Volumes - click Autoconfigure to create the volume automatically.
17. This is now complete.
18. Go into Disk Management and you will see the new disk.
19. Right click it to set it Online, and then right click again to Initialize Disk. From there you can create a new simple volume as normal or whatever your partitioning needs.
20. At this point re-enable the primary NIC if you had to previously disable it.

How to re-create the secure channel

We recently had an incident where a CA on a test domain had its computer account deleted. As it was the CA, we couldn't drop it from the domain and rejoin it (system properties showed "Note: The identification of the computer cannot be changed because: - The Certification Authority is installed on this computer."

To solve the issue, I recreated the computer account manually.
Then, on the server itself I reset the machine password a couple of times using:
netdom resetpwd /Server:name of DC /UserD:domain user /PasswordD:password

Then, I reset the secure channel. This is the part that actually fixed the problem:
netdom reset computer to reset /Domain:DNS name of domain /Server:name of DC /UserO:domain user /PasswordO:password

After that, nltest /SC_QUERY:DNS name of domain shows that the secure channel is operative again.

Refreshing Group Membership Without Logging Off and On Again

I haven't done much investigation into what limitations there are with this (for instance, does group policy filtered to a an added security group take effect), but klist allows you to get a new kerberos ticket, with any new access rights added, without logging off and on again.

Run: klist purge - this will purge the existing kerberos ticket.
klist tgt - TGT refresh, should display the ticket.

The user can now access any resources secured by groups they have been added to since they last logged on.

Tools like whoami /groups will still not display the new group membership, but will if you create a new cmd window using runas since the process will be created using the updated security token.
It may be that by launching a new cmd in this way ansd then running gpupdate, that this will also allow group policies targeted to any new groups to also take effect.

TGT Refresh v TGT renewal
Using klist in this way refreshes the TGT, and new group memberships are added.
A TGT is renewed by default every 10 hours, but this will not add the new group memberships as it only extends the old TGT's validity. After 7 days, TGT refresh happens and the new memberships will be added.

VAMT

This is the Volume Activation Management Tool. When KMS is not an option (Technet subscriptions do not provide KMS keys), VAMT can provide a good alternative using MAK keys.

This article describes how I set up VAMT to activate VMs running on a VirtualBox host-only environment. In this example, VMs will be activated using the VAMT server as a proxy.

1. Install a Windows Server 2008 R2 server with both host-only and bridged network adapters.
2. Install VAMT.
3. Open the console and choose how to locate machines (searching AD for example).
4. Once the scan finds some machines, they will be in the "Status Unknown" section on the left hand side of the user interface. At this stage no license scanning has taken place.
5. Highlight a machine, right click and choose "Update Status". You will be able to do this either using the current credentials with which you are logged on with, or you can specify alternative credentials. Ultimately you need to perform this operation with an account with local admin privileges on the remote machine.
6. Once scanned the machine will be placed in either the Licensed, Not Licensed or Unmanaged sections on the left.
7. You can add a product key by entering it in the relevant place (it also requires a description). Click "Add Product Key".
8. You can then right click on the remote computer and choose "Install Product Key".
9. If the remote client has internet connectivity you can then right click on it and choose Activate - Online Activate. Since in this example the remote computers are on a host-only network, I will set up the VAMT as the proxy activation server. to do this, right click on the remote machine and choose Activate - Proxy Activate. The VAMT will then activate on the client's behalf.
10. Once done, save the configuration of VAMT, otherwise you'll tend to find the computers won't be there when you next open it, and neither will the product keys. To do this, choose "Save List as" to save the cli file. Next time you go into VAMT, open this file.

AD Searches with DistinguishedName

I've seen this with both LDAP filters and Get-ADUser:
It seems that you cannot use wildcards when searching with distinguishedName.
So for example the following is not valid:

Get-ADUser -Filter 'distinguishedName -like "CN*"'

The only valid use of wildcards with distinguishedName is to test for existence or non-existence of the value.

e.g. Get-ADUser -Filter 'distinguishedName -like "*"'

The easiest way I have seen to do this is with ADFIND and use the -excldn switch

e.g. adfind -excldn "OU=Admin Accounts,OU=User Management";"OU=Shared Accounts,OU=User Management" -b "OU=User Management,DC=test,DC=com" -f "(&(objectCategory=Person)(objectClass=User))" dn

This will show you just the dn's for the users that are under the OU=User Management,DC=test,DC=com OU structure, but excluding any that have either "OU=Admin Accounts,OU=User Management" or "OU=Shared Accounts,OU=User Management" in their distinguished names.

Challenge - Response authentication in Windows

Specifically, we're talking about LanMan and NTLM responses.
LanMan is really for pre-NT4 clients but has been included for backwards compatibility since then.

Format for challenge-response authentication

1. Client sends a type 1 (NEGOTIATE_MESSAGE) to server, advertising its capabilities.
2. Server sends type 2 (CHALLENGE_MESSAGE) which includes supported features and the challenge itself.
3. Client replies with type 3 (AUTHENTICATION_MESSAGE) which contains information about the client including domain and user name plus 1 or more responses to the challenge.

LanMan responses

1. The ASCII password is converted to upper case.
2. It is then null padded to 14 bytes.
3. Split into 2 x 7 bytes.
4. These are used to create 2 DES keys.
5. Each of these keys is used to DES-encrypt the constant ASCII string, resulting in 2 x 8 byte ciphertext values. These 2 ciphertext values are concatenated to a 16 byte value. THIS IS THE LM HASH.
6. The 16 byte LM hash is null padded to 21 bytes.
7. This is split into 3 x 7 bytes.
8. These values are then used to create 3 DES keys.
9. Each of these keys is used to DES-encrypt the challenge in the type 2 challenge message. It results in 3 x 8 byte ciphertext values that can be concatenated to form a 24 byte value. THIS IS THE LM RESPONSE.

Weaknesses

• Converted to upper case so all of that complexity is lost.
• If password is 7 characters or fewer, the second value is null, so straight-away half of the LM hash is compromised.
• Not true one-way encryption as password can be obtained from the hash.
• Since LM hashonly changes when password changes, susceptible to pass the hash attacks, where an attacker uses the hash directly to authenticate to a server rather than having to brute force the hashes to obtain the clear text password. This is also true for NTLM authentication. Both NTLM and LM are password equivalent so if you can get the hash from the server you never need to know the actual password.

If the user's password is > 15 characters then the DC will not store the LM hash so the LM response cannot be used to authenticate the user. The LM response is still generated but a 16 byte null value is used as the LM hash in the calculation and then ignored by the server.

NTLM v1

1. Server sends 8 byte challenge.
2. Client uses a shared secret between the client and server, specifically one of the hashes (LM or NT) to return a 24 byte result of this computation.
3. NTLMv1 computations are usually made for both hashes with both 24 byte results sent to the server, unless you configure it not to.
4. Server verifies that the client has computed the correct result. This assumes that they then have possession of the secret and so are authenticated.
5. Both hashes produce 16 byte values.
6. 5 bytes of zeroes appended to them.
7. Separated into 3 x 7 bytes (56 bits). Each of these 56 bit values is used as a key to DES-encrypt teh 64 bit (8 byte) challenge. The 3 encryptions are reunited to form the 24 byte response.

NTLM v2

1. Server sends 8 byte challenge.
2. Client sends 2 x 16 byte response.
3. This response is the HMAC-MD5 hash of the server challenge, a randomly generated client challenge, and a HMAC-MD5 hash of the user's password and other identifying information.
4. The first response is shorter: it's an 8 byte random value for the client challenge. To verify this response the server must receive as part of the response the client challenge. The 8 byte client challenge is appended to the 16 byte response to make a 24 byte package.
5. The second response is a variable length client challenge which includes the current time, an 8 byte random value, domain name and some standard stuff. The response must include a  copy of this client challenge and is therefore of variable length.

NTLM Weaknesses

• As pointed out above, it's susceptible to pass the hash attacks.
• In Feb 2010 several flaws in the Windows implementation of NTLM were proved: one attack included the ability to predict the random numbers/challenges generated by the protocol. These flaws were fixed by MS010-012.

Why Not Just Use Kerberos?

Kerberos relies on a trusted third party. If one is not available (for example where a client is not a member of a domain, local accounts and authentication to an untrusted domain), then NTLM still rules!