Script to schedule Nessus scans based around the Microsoft patch cycle

Set-NessusFolderScanSchedule.ps1

<#
.SYNOPSIS
    Schedule Nessus scans based around the Microsoft patch cycle
#>

[CmdletBinding()]
Param(
    [Parameter(Mandatory=$true)][String]$ComputerName,
    [Int]$Port = 8834,
    [Parameter(Mandatory=$true)][String]$ScanFolder,
    [Parameter(Mandatory=$true)][DateTime]$RangeStartTime,
    [Parameter(Mandatory=$true)][DateTime]$RangeEndTime,
    [Parameter(Mandatory=$true)][Int]$PatchTuesdayOffset,
    [Bool]$EmailNotify=$false,
    [String[]]$SendTo,
    [PSCredential]$Credential,
    [String]$AccessKey,
    [String]$SecretKey
)

# Simplified Get-PatchTuesday, returns based on current month
function Get-PatchTuesday {
    # Calculate patch tuesday for this month
    $baseDate = Get-Date (Get-Date -Format "yyyy-MM-01")
    (0..30 | ForEach-Object {$baseDate.AddDays($_)} | Where-Object {$_.DayOfWeek -like "Tue*"})[1]
}

# Get the patch and scan dates
$patchTuesday = Get-PatchTuesday
$scanDate = $patchTuesday.AddDays($PatchTuesdayOffset)

# Set the static nessus parameters
$nessusParams = @{
    ComputerName = $ComputerName
    Port = $Port
}

# Add the credentials or API keys
if ($Credential) {
    $nessusParams.Credentials = $Credential
}
elseif ($AccessKey -and $SecretKey) {
    $nessusParams.AccessKey = $AccessKey
    $nessusParams.SecretKey = $SecretKey
}
else {
    Write-Error 'No credentials or API keys provided'
    Return
}

# Initialize a session with Nessus
$session = New-NessusSession @nessusParams

# Get all of the scan folders
$scanFolders = Get-NessusFolder -SessionId $session.SessionId

# Get the target folder and the scan IDs within
$targetFolder = $scanFolders.Where{$_.Name -eq $ScanFolder}
if (!$targetFolder) {Write-Error "Folder: $ScanFolder not found."}
[Array]$targetScans = Get-NessusScan -SessionId $session.SessionId -FolderId $targetFolder.FolderId

# Add a day to datetimes if the end time is in the next day
if ($RangeEndTime.Hour -lt $RangeStartTime.Hour) {
    $RangeEndTime = $RangeEndTime.AddDays(1)
    $scanEndDate = $scanDate.AddDays(1)
} else {
    $scanEndDate = $scanDate
}

# Calculate the start time
$startYMD = $scanDate.ToString('yyyy-MM-dd')
$startHM = $RangeStartTime.ToString('HH:mm')
$startDateTime = Get-Date ("$startYMD $startHM")

# Calculate the end time
$endYMD = $scanEndDate.ToString('yyyy-MM-dd')
$endHM = $RangeEndTime.ToString('HH:mm')
$endDateTime = Get-Date ("$endYMD $endHM")

# Calculate the time span
$timeSpan = New-TimeSpan -Start $startDateTime -End $endDateTime
$msOffset = $timeSpan.TotalMilliseconds / ($targetScans.Count - 1)

# Iterate through scans, scheduling across the time range
$scheduledScans = $targetScans.ForEach{
    # Offset the scan
    $currentScan = $targetScans.IndexOf($_)
    if ($targetScans.Count -gt 1) {
        $scanStart = $startDateTime.AddMilliseconds($msOffset * $currentScan)
    } else {
        $scanStart = $startDateTime
    }
    $scan = Set-NessusScanSchedule -SessionId $session.SessionId -ScanId $_.ScanId -StartTime $scanStart
    [PSCustomObject]@{
        'Scan' = $_.name
        'Start Time' = $scanStart.ToString('yyyy-MM-dd HH:mm:ss')
    }
}

# Send an email if the setting is enabled
if ($EmailNotify -and $SendTo) {
     $html = Get-Content "$PSScriptRoot\Resources\ScheduleEmailTemplate.html"
     $html = $html.Replace('$schedule',"$($startDateTime.ToString('yyyy-MM-dd HH:mm:ss')) to $($endDateTime.ToString('yyyy-MM-dd HH:mm:ss'))")
     $html = $html.Replace('$table',($scheduledScans | ConvertTo-Html -Fragment))

     $emailParams = @{
         SmtpServer = 'azmtaprd01.az.int'
         From = 'No Reply <noreply@azdoa.gov>'
         To = $SendTo
         Subject = "Nessus Scan Scheduling - $ScanFolder"
         Body = $html -join "`n"
         BodyAsHtml = $true
     }
     Send-MailMessage @emailParams
}