Powershell script to change local admin password

powershell

I have a script that I am using to change the local admin password from Microsoft. https://support.microsoft.com/en-us/kb/2962486?wa=wsignin1.0 is where I found it. Here is the script for anyone too lazy to click:

function Invoke-PasswordRoll
{
<#
.SYNOPSIS

This script can be used to set the local account passwords on remote machines to random passwords. The 

username/password/server combination will be saved in a CSV file.
The account passwords stored in the CSV file can be encrypted using a password of the administrators choosing to 

ensure clear-text account passwords aren't written to disk.
The encrypted passwords can be decrypted using another function in this file: ConvertTo-CleartextPassword


Function: Invoke-PasswordRoll
Author: Microsoft
Version: 1.0

.DESCRIPTION

This script can be used to set the local account passwords on remote machines to random passwords. The 

username/password/server combination will be saved in a CSV file.
The account passwords stored in the CSV file can be encrypted using a password of the administrators choosing to 

ensure clear-text account passwords aren't written to disk.
The encrypted passwords can be decrypted using another function in this file: ConvertTo-CleartextPassword

.PARAMETER ComputerName

An array of computers to run the script against using PowerShell remoting.

.PARAMETER LocalAccounts

An array of local accounts whose password should be changed.

.PARAMETER TsvFileName

The file to output the username/password/server combinations to.

.PARAMETER EncryptionKey

A password to encrypt the TSV file with. Uses AES encryption. Only the passwords stored in the TSV file will be 

encrypted, the username and servername will be clear-text.

.PARAMETER PasswordLength

The length of the passwords which will be randomly generated for local accounts.

.PARAMETER NoEncryption

Do not encrypt the account passwords stored in the TSV file. This will result in clear-text passwords being 

written to disk.

.EXAMPLE

. .\Invoke-PasswordRoll.ps1    #Loads the functions in this script file
Invoke-PasswordRoll -ComputerName (Get-Content computerlist.txt) -LocalAccounts @

("administrator","CustomLocalAdmin") -TsvFileName "LocalAdminCredentials.tsv" -EncryptionKey "Password1"

Connects to all the computers stored in the file "computerlist.txt". If the local account "administrator" and/or 

"CustomLocalAdmin" are present on the system, their password is changed
to a randomly generated password of length 20 (the default). The username/password/server combinations are 

stored in LocalAdminCredentials.tsv, and the account passwords are AES encrypted using the password "Password1".

.EXAMPLE

. .\Invoke-PasswordRoll.ps1    #Loads the functions in this script file
Invoke-PasswordRoll -ComputerName (Get-Content computerlist.txt) -LocalAccounts @("administrator") -TsvFileName 

"LocalAdminCredentials.tsv" -NoEncryption -PasswordLength 40

Connects to all the computers stored in the file "computerlist.txt". If the local account "administrator" is 

present on the system, its password is changed to a random generated
password of length 40. The username/password/server combinations are stored in LocalAdminCredentials.tsv 

unencrypted.

.NOTES
Requirements: 
-PowerShellv2 or above must be installed
-PowerShell remoting must be enabled on all systems the script will be run against

Script behavior:
-If a local account is present on the system, but not specified in the LocalAccounts parameter, the script will 

write a warning to the screen to alert you to the presence of this local account. The script will continue 

running when this happens.
-If a local account is specified in the LocalAccounts parameter, but the account does not exist on the computer, 

nothing will happen (an account will NOT be created).
-The function ConvertTo-CleartextPassword, contained in this file, can be used to decrypt passwords that are 

stored encrypted in the TSV file.
-If a server specified in ComputerName cannot be connected to, PowerShell will output an error message.
-Microsoft advises companies to regularly roll all local and domain account passwords.

#>
    [CmdletBinding(DefaultParameterSetName="Encryption")]
    Param(
        [Parameter(Mandatory=$true)]
        [String[]]
        $ComputerName,

        [Parameter(Mandatory=$true)]
        [String[]]
        $LocalAccounts,

        [Parameter(Mandatory=$true)]
        [String]
        $TsvFileName,

        [Parameter(ParameterSetName="Encryption", Mandatory=$true)]
        [String]
        $EncryptionKey,

        [Parameter()]
        [ValidateRange(20,120)]
        [Int]
        $PasswordLength = 20,

        [Parameter(ParameterSetName="NoEncryption", Mandatory=$true)]
        [Switch]
        $NoEncryption
    )


    #Load any needed .net classes
    Add-Type -AssemblyName "System.Web" -ErrorAction Stop


    #This is the scriptblock that will be executed on every computer specified in ComputerName
    $RemoteRollScript = {
        Param(
            [Parameter(Mandatory=$true, Position=1)]
            [String[]]
            $Passwords,

            [Parameter(Mandatory=$true, Position=2)]
            [String[]]
            $LocalAccounts,

            #This is here so I can record what the server name that the script connected to was, sometimes the 

DNS records get messed up, it can be nice to have this.
            [Parameter(Mandatory=$true, Position=3)]
            [String]
            $TargettedServerName
        )

        $LocalUsers = Get-WmiObject Win32_UserAccount -Filter "LocalAccount=true" | Foreach {$_.Name}

        #Check if the computer has any local user accounts whose passwords are not going to be rolled by this 

script
        foreach ($User in $LocalUsers)
        {
            if ($LocalAccounts -inotcontains $User)
            {
                Write-Warning "Server: '$($TargettedServerName)' has a local account '$($User)' whos password is 

NOT being changed by this script"
            }
        }

        #For every local account specified that exists on this server, change the password
        $PasswordIndex = 0
        foreach ($LocalAdmin in $LocalAccounts)
        {
            $Password = $Passwords[$PasswordIndex]

            if ($LocalUsers -icontains $LocalAdmin)
            {
                try
                {
                    $objUser = [ADSI]"WinNT://localhost/$($LocalAdmin), user"
                    $objUser.psbase.Invoke("SetPassword", $Password)

                    $Properties = @{
                        TargettedServerName = $TargettedServerName
                        Username =  $LocalAdmin
                        Password = $Password
                        RealServerName = $env:computername
                    }

                    $ReturnData = New-Object PSObject -Property $Properties
                    Write-Output $ReturnData
                }
                catch
                {
                    Write-Error "Error changing password for user:$($LocalAdmin) on server:

$($TargettedServerName)"
                }
            }

            $PasswordIndex++
        }
    }


    #Generate the password on the client running this script, not on the remote machine. System.Web.Security 

isn't available in the .NET Client profile. Making this call
    #    on the client running the script ensures only 1 computer needs the full .NET runtime installed (as 

opposed to every system having the password rolled).
    function Create-RandomPassword
    {
        Param(
            [Parameter(Mandatory=$true)]
            [ValidateRange(20,120)]
            [Int]
            $PasswordLength
        )

        $Password = [System.Web.Security.Membership]::GeneratePassword($PasswordLength, $PasswordLength / 4)

        #This should never fail, but I'm putting a sanity check here anyways
        if ($Password.Length -ne $PasswordLength)
        {
            throw new Exception("Password returned by GeneratePassword is not the same length as required. 

Required length: $($PasswordLength). Generated length: $($Password.Length)")
        }

        return $Password
    }


    #Main functionality - Generate a password and remote in to machines to change the password of local accounts 

specified
    if ($PsCmdlet.ParameterSetName -ieq "Encryption")
    {
        try
        {
            $Sha256 = new-object System.Security.Cryptography.SHA256CryptoServiceProvider
            $SecureStringKey = $Sha256.ComputeHash([System.Text.UnicodeEncoding]::Unicode.GetBytes

($EncryptionKey))
        }
        catch
        {
            Write-Error "Error creating TSV encryption key" -ErrorAction Stop
        }
    }

    foreach ($Computer in $ComputerName)
    {
        #Need to generate 1 password for each account that could be changed
        $Passwords = @()
        for ($i = 0; $i -lt $LocalAccounts.Length; $i++)
        {
            $Passwords += Create-RandomPassword -PasswordLength $PasswordLength
        }

        Write-Output "Connecting to server '$($Computer)' to roll specified local admin passwords"
        $Result = Invoke-Command -ScriptBlock $RemoteRollScript -ArgumentList @($Passwords, $LocalAccounts, 

$Computer) -ComputerName $Computer
        #If encryption is being used, encrypt the password with the user supplied key prior to writing to disk
        if ($Result -ne $null)
        {
            if ($PsCmdlet.ParameterSetName -ieq "NoEncryption")
            {
                $Result | Select-Object Username,Password,TargettedServerName,RealServerName | Export-Csv -

Append -Path $TsvFileName -NoTypeInformation
            }
            else
            {
                #Filters out $null entries returned
                $Result = $Result | Select-Object Username,Password,TargettedServerName,RealServerName

                foreach ($Record in $Result)
                {
                    $PasswordSecureString = ConvertTo-SecureString -AsPlainText -Force -String 

($Record.Password)
                    $Record | Add-Member -MemberType NoteProperty -Name EncryptedPassword -Value (ConvertFrom-

SecureString -Key $SecureStringKey -SecureString $PasswordSecureString)
                    $Record.PSObject.Properties.Remove("Password")
                    $Record | Select-Object Username,EncryptedPassword,TargettedServerName,RealServerName | 

Export-Csv -Append -Path $TsvFileName -NoTypeInformation
                }
            }
        }
    }
}


function ConvertTo-CleartextPassword
{
<#
.SYNOPSIS
This function can be used to decrypt passwords that were stored encrypted by the function Invoke-PasswordRoll.

Function: ConvertTo-CleartextPassword
Author: Microsoft
Version: 1.0

.DESCRIPTION
This function can be used to decrypt passwords that were stored encrypted by the function Invoke-PasswordRoll.


.PARAMETER EncryptedPassword

The encrypted password that was stored in a TSV file.

.PARAMETER EncryptionKey

The password used to do the encryption.


.EXAMPLE

. .\Invoke-PasswordRoll.ps1    #Loads the functions in this script file
ConvertTo-CleartextPassword -EncryptionKey "Password1" -EncryptedPassword 

76492d1116743f0423413b16050a5345MgB8AGcAZgBaAHUAaQBwADAAQgB2AGgAcABNADMASwBaAFoAQQBzADEAeABjAEEAPQA9AHwAZgBiAGYA

MAA1ADYANgA2ADEANwBkADQAZgAwADMANABjAGUAZQAxAGIAMABiADkANgBiADkAMAA4ADcANwBhADMAYQA3AGYAOABkADcAMQA5ADQAMwBmAGYA

NQBhADEAYQBjADcANABkADIANgBhADUANwBlADgAMAAyADQANgA1ADIAOQA0AGMAZQA0ADEAMwAzADcANQAyADUANAAzADYAMAA1AGEANgAzADEA

MQA5ADAAYwBmADQAZAA2AGQA"

Decrypts the encrypted password which was stored in the TSV file.

#>
    Param(
        [Parameter(Mandatory=$true)]
        [String]
        $EncryptedPassword,

        [Parameter(Mandatory=$true)]
        [String]
        $EncryptionKey
    )

    $Sha256 = new-object System.Security.Cryptography.SHA256CryptoServiceProvider
    $SecureStringKey = $Sha256.ComputeHash([System.Text.UnicodeEncoding]::Unicode.GetBytes($EncryptionKey))

    [SecureString]$SecureStringPassword = ConvertTo-SecureString -String $EncryptedPassword -Key 

$SecureStringKey
    Write-Output ([System.Runtime.InteropServices.Marshal]::PtrToStringAuto

([System.Runtime.InteropServices.Marshal]::SecureStringToCoTaskMemUnicode($SecureStringPassword)))
}

When I run the script using:

Invoke-PasswordRoll -ComputerName (Get-Content computerlist.txt) -LocalAccounts @("administrator","CustomLocalAdmin") -TsvFileName "LocalAdminCredentials.tsv" -EncryptionKey "Password1"

it changes the password on the targeted computers, but it doesn't change it to "Password1". What exactly is this script doing?

Best Answer

Like Tomasz and Zoredache said: the script Microsoft provides can only be used to set the local account passwords on remote machines to random passwords. The account passwords stored in the CSV file can be encrypted using a password of the administrators choosing (the parameter -EncryptionKey) to ensure clear-text account passwords aren't written to disk.

The encrypted passwords (stored in the TSV file) can be decrypted using another function in the same file: ConvertTo-CleartextPassword.

In our environment we also would like to change the password regularly, so we created two scripts: one to create a new file with an encrypted password (of our own choosing) and distributed this file to all of our workstations. A seconds script (distributed also to the workstations) runs every X hours and resets the password based on the contents of the file. Of course the password used to encrypt and decrypt is still stored in plain text, but the password itself isn't. This way you really need to know what you are doing to retrieve the Local Admin password en because the encryption file and script are saved in different locations it is pretty safe.

Create the password file

We use the following script (I stripped out the error logging and try/catches) to create a password file:

$LocalAdminPW = "0urAdminP@ssword" #the password that is used to set as the local admin password
$EncryptionPW = "0urEncryptionP@ssword" #password to encrypt and decrypt the password
$File = "C:\Temp\Password.tsv" #file to create

#Create encryption key
$Sha256 = new-object System.Security.Cryptography.SHA256CryptoServiceProvider
$SecureStringKey = $Sha256.ComputeHash([System.Text.UnicodeEncoding]::Unicode.GetBytes($EncryptionPW))

#Encrypt the password with the user supplied encryption password
PasswordSecureString = ConvertTo-SecureString -AsPlainText -Force -String $LocalAdminPW

#Create TSV-File with the encrypted password
ConvertFrom-SecureString -Key $SecureStringKey -SecureString $PasswordSecureString | Out-File -Force -FilePath "$File"

#Gathering the new encrypted password for the local administrator account
$LocalAdminPW = Get-Content $FileLocation

Set Local Admin Password with the created password file

We use the following script to decrypt the password from the password file and use this to set the Administrator password (I stripped the error handling and logging):

#function to get decrypted password
Function Get-DecryptedPassword {
    [CmdletBinding()]
    param(
        $EncryptedPW,
        $LocalAdminPW
    )

    #Decrypt the password with the user supplied encryption password
    $Sha256 = new-object System.Security.Cryptography.SHA256CryptoServiceProvider
    $SecureStringKey = $Sha256.ComputeHash([System.Text.UnicodeEncoding]::Unicode.GetBytes($EncryptionPW))
    [SecureString]$SecureStringPassword = ConvertTo-SecureString -String $LocalAdminPW -Key $SecureStringKey
    return ([System.Runtime.InteropServices.Marshal]::PtrToStringAuto([System.Runtime.InteropServices.Marshal]::SecureStringToCoTaskMemUnicode($SecureStringPassword)))
}

#Change password local admin account
$LocalAdmin = "Administrator"
$objUser = [ADSI]"WinNT://localhost/$($LocalAdmin), user"
$objUser.psbase.Invoke("SetPassword", (Get-DecryptedPassword -EncryptedPW $EncryptionPW  -LocalAdminPW $LocalAdminPW))

Best Answer

Create the password file

Set Local Admin Password with the created password file

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