This is a guide to the following problem (not exclusive but here) on Windows:
Users need our support and we supporters often use global administrative accounts to do this. Using these accounts safely is a real challenge.
Any admin who takes security seriously fears attacks by his own colleagues. Thus he faces a small dilemma with user support: strictly speaking, each user PC is "enemy territory". We do not know if the user has evil intentions and might have prepared his already compromised machine, only waiting for us. How to authenticate there without running the risk that the user will somehow capture our password or hash?
Many questions arise:
You can find various recommendations also by Microsoft but I want to exhibit and recommend my own approach here. It comes without two-factor authentication, without additional software and is robust. I have been using it for more than a year now.
The main idea is: there is no need to use an account that is admin on more machines than the supported one! We are working on one (1) machine, so why should we use an account that is admin on all clients? The reason is convenience. And we pay for that laziness -- anyone familiar with mimikatz and similar exploitation tools will agree. I will show an alternate way that is secure and still convenient.
The usage scenario: User needs support, the problem has been identified: it is not a user profile problem so we will not need to work inside the user's session, but unfortunately, admin rights are needed to fix it. Still, the goal is to leave no exploitable credentials on the supported computer.
My intention is
Now let's start:
Step 1: For each PC ("somePC") I automatically create a disabled user account "adminsomePC" with a random password that can log on nowhere. Therefore the parameter logonworkstations is set to some fantasy name (here: fantasynamehere). We can create a list.txt with all pc names inside and then run the following at the DC:
for /f %a in (list.txt) do net user /add admin%a /random /active:no /WORKSTATIONS:fantasynamehere
Step 2: These accounts will live in a their own OU, to which (weak) support employee accounts get delegated full rights (using the delegation of control wizard) in order to set those admin accounts active/inactive.
Step 3: A domain startup script makes the corresponding account member of the local admin group:
net localgroup /add administrators admin%computername%
Step 4: If a supporter needs admin rights on somePC, he activates that somePCadmin account scripted (see below), lets the script set a new password and at the same time enter these credentials in the credential manager of his own computer and automatically set up a remote desktop connection to the PCxy. When he's done, the support account is disabled automatically.
The script itself is simple batch code, refined with a PowerShell script scripts.zip\Day6-PowerShell\GenerateRandomPassword.ps1 (public domain) from http://www.sans.org/windows-security/files/scripts.zip that generates random passwords (adjustable length, default: 15).
@echo off
set /p target=What machine?: %=%
for /f %%a in ('powershell \\server\share\GenerateRandomPassword.ps1') do net user admin%target% %%a /domain /active /workstations:%computername%,%target% & cmdkey /add:TERMSRV/%target% /user:netbiosdomainname\admin%target% /pass:%%a
start mstsc /v:%target%
pause
net user admin%target% /active:no /domain
The account can be used to help via RDP completely safely. If you correctly terminate the batch by pressing any key, that account will be deactivated immediately again. But just in case you should create a task that deactivates all support admins after working hours and schedule it to run on your DC. I had to minimally edit GenerateRandomPassword.ps1 to fit my needs. I commented out line 65:
#1..20 | foreach { Generate-RandomPassword -length $length } ; "`n"
and I added:
1 | foreach { Generate-RandomPassword -length $length } ; "`n"
That's it.
Certainly you can further refine this, my intent is to provide the base.
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Which common task do I pick "Create, delete and manage accounts"? Or, do I pick Create Custom Task?
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