<#
.TITLE
    Local Admin Drift Remediation Script

.SYNOPSIS
    Removes unauthorized members from the local Administrators group.

.DESCRIPTION
    Enumerates the local Administrators group and removes every member that is not
    on the allowlist: the built-in Administrator (RID 500), the Entra device
    administrator role SIDs, Domain/Enterprise Admins for hybrid devices, and the
    configurable allowed account names. Removed members are logged in the output so
    the remediation history in Intune shows exactly what changed. Paired with
    detect-local-admin-drift.ps1.

.TAGS
    Remediation,Action

.REMEDIATIONTYPE
    Remediation

.PAIRSCRIPT
    detect-local-admin-drift.ps1

.PLATFORM
    Windows

.MINROLE
    Intune Service Administrator

.PERMISSIONS
    DeviceManagementManagedDevices.ReadWrite.All

.AUTHOR
    Ugur Koc

.VERSION
    1.0

.CHANGELOG
    1.0 - Initial release

.LASTUPDATE
    2026-07-20

.EXAMPLE
    .\remediate-local-admin-drift.ps1
    Removes all unauthorized members from the local Administrators group

.NOTES
    - Runs in SYSTEM context via Intune Remediations
    - Keep $AllowedNames identical to the detection script or the pair will fight each other
    - Removal uses the group's Remove method via ADSI, which also handles orphaned SIDs
    - Test on a pilot group first: removing an account that users rely on locks them out of admin tasks
#>

$ErrorActionPreference = "Stop"

# Account names that are allowed local admins (keep in sync with detection script)
$AllowedNames = @(
    "LocalAdmin"
)

function Get-AdministratorsGroup {
    $adminGroupSid = "S-1-5-32-544"
    $groupName = (Get-LocalGroup -SID $adminGroupSid).Name
    return [ADSI]"WinNT://./$groupName,group"
}

function Test-AllowedMember {
    param([object]$Member)

    if ($Member.Sid -and $Member.Sid -match "-500$") { return $true }
    if ($Member.Sid -and $Member.Sid -like "S-1-12-1-*") { return $true }
    if ($Member.Sid -and ($Member.Sid -match "-512$" -or $Member.Sid -match "-519$")) { return $true }
    if ($AllowedNames -contains $Member.Name) { return $true }

    return $false
}

try {
    $group = Get-AdministratorsGroup

    $members = @($group.Invoke("Members")) | ForEach-Object {
        $adsiMember = [ADSI]$_
        $sid = $null
        try {
            $sidBytes = $adsiMember.InvokeGet("objectSID")
            $sid = (New-Object System.Security.Principal.SecurityIdentifier($sidBytes, 0)).Value
        }
        catch {
            # Orphaned entries may not expose a SID
        }
        [PSCustomObject]@{
            Name    = $adsiMember.InvokeGet("Name")
            AdsPath = $adsiMember.InvokeGet("AdsPath")
            Sid     = $sid
        }
    }

    $removed = [System.Collections.Generic.List[string]]::new()
    $failed = [System.Collections.Generic.List[string]]::new()

    foreach ($member in @($members)) {
        if (Test-AllowedMember -Member $member) { continue }

        try {
            $group.Remove($member.AdsPath)
            $removed.Add($member.Name)
        }
        catch {
            $failed.Add("$($member.Name): $($_.Exception.Message)")
        }
    }

    if ($removed.Count -gt 0) {
        Write-Output "Removed from local Administrators: $($removed -join ', ')"
    }
    else {
        Write-Output "No unauthorized members needed removal."
    }

    if ($failed.Count -gt 0) {
        Write-Output "Failed to remove: $($failed -join ' | ')"
        exit 1
    }

    exit 0
}
catch {
    Write-Error $_
    exit 1
}

# Copia sin cambios de https://github.com/ugurkocde/IntuneAutomation (commit 797bb2e).
# MIT License
#
# Copyright (c) 2025 Ugur Koc | Microsoft MVP
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.