Patch

CVE-2021-34527

with vRx

Vulnerability Overview

CVE Name

CVE-2021-34527

Severity

8.8

High

CVE Description

<p>A remote code execution vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could...</p>

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Latest Patch info

Patch Name

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34527

Date

03.07.2021

Script

Script Type

Remediation script

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The following script has 2 options first option is to disable the spooler services if it's not used according to the admin choice, And the 2nd option is to apply mitigations by checking for some register keys that helps in reduce and mitigate the exploitation of the vulnerability such as "\Software\Policies\Microsoft\Windows NT\Printers\PointAndPrint\RestrictDriverInstallationToAdministrators" which is determine whether only administrators can install printer drivers that are not digitally signed. "\Software\Policies\Microsoft\Windows NT\Printers\PointAndPrint\NoElevationOnInstall" Which is determine whether Point and Print installations for printer drivers require elevated permissions, "\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\EnableLUA" Which is determine whether User Account Control (UAC) prompts for consent or credentials are displayed for all users when executing applications that require administrator permissions. Note: Run script as admin.

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# Define the action to execute.
# Possible values: "DisableSpooler", "ApplyMitigations", or "Both"
$action = "Both"

# If $action is "DisableSpooler" or "Both", disable the Spooler service.
if ($action -eq "DisableSpooler" -or $action -eq "Both") {
    Stop-Service -Name Spooler -Force
    Set-Service -Name Spooler -StartupType Disabled
    Write-Output "[+] Spooler service has been disabled."
}

# If $action is "ApplyMitigations" or "Both", apply the registry mitigations.
if ($action -eq "ApplyMitigations" -or $action -eq "Both") {

# Configuration for "NoElevationOnInstall" in PointAndPrint
    $ppRegSubkey    = "HKLM:\Software\Policies\Microsoft\Windows NT\Printers\PointAndPrint"
    $ppRegValueName = "NoElevationOnInstall"
    $ppRegValueType = "DWord"
    $ppRegValueData = 0

# Configuration for "EnableLUA" in System
    $luRegSubkey    = "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System"
    $luRegValueName = "EnableLUA"
    $luRegValueType = "DWord"
    $luRegValueData = 1

# Configuration for "RestrictDriverInstallationToAdministrators" in PointAndPrint
    $regSubkey    = "HKLM:\Software\Policies\Microsoft\Windows NT\Printers\PointAndPrint"
    $regValueName = "RestrictDriverInstallationToAdministrators"
    $regValueType = "DWord"
    $regValueData = 1

# --- Update NoElevationOnInstall ---
    if ((Test-Path $ppRegSubkey) -and (Get-ItemProperty -Path $ppRegSubkey -Name $ppRegValueName -ErrorAction SilentlyContinue)) {
        $ppRegValue = Get-ItemProperty -Path $ppRegSubkey -Name $ppRegValueName
        if ($ppRegValue.$ppRegValueName -ne $ppRegValueData) {
            Set-ItemProperty -Path $ppRegSubkey -Name $ppRegValueName -Value $ppRegValueData -Type $ppRegValueType
            Write-Output "[+] The registry value '$ppRegValueName' in subkey '$ppRegSubkey' has been updated to $ppRegValueData."
        }
        else {
            Write-Output "[-] The registry value '$ppRegValueName' in subkey '$ppRegSubkey' already exists and is set to $ppRegValueData."
        }
    }
    else {
        New-Item -Path $ppRegSubkey -Force | Out-Null
        New-ItemProperty -Path $ppRegSubkey -Name $ppRegValueName -Value $ppRegValueData -PropertyType $ppRegValueType | Out-Null
        Write-Output "[+] The registry value '$ppRegValueName' in subkey '$ppRegSubkey' has been created and set to $ppRegValueData."
    }

# --- Update EnableLUA ---
    if ((Test-Path $luRegSubkey) -and (Get-ItemProperty -Path $luRegSubkey -Name $luRegValueName -ErrorAction SilentlyContinue)) {
        $luRegValue = Get-ItemProperty -Path $luRegSubkey -Name $luRegValueName
        if ($luRegValue.$luRegValueName -ne $luRegValueData) {
            Set-ItemProperty -Path $luRegSubkey -Name $luRegValueName -Value $luRegValueData -Type $luRegValueType
            Write-Output "[+] The registry value '$luRegValueName' in subkey '$luRegSubkey' has been updated to $luRegValueData."
        }
        else {
            Write-Output "[-] The registry value '$luRegValueName' in subkey '$luRegSubkey' already exists and is set to $luRegValueData."
        }
    }
    else {
        New-Item -Path $luRegSubkey -Force | Out-Null
        New-ItemProperty -Path $luRegSubkey -Name $luRegValueName -Value $luRegValueData -PropertyType $luRegValueType | Out-Null
        Write-Output "[+] The registry value '$luRegValueName' in subkey '$luRegSubkey' has been created and set to $luRegValueData."
    }

# --- Update RestrictDriverInstallationToAdministrators ---
    if ((Test-Path $regSubkey) -and (Get-ItemProperty -Path $regSubkey -Name $regValueName -ErrorAction SilentlyContinue)) {
        $regValue = Get-ItemProperty -Path $regSubkey -Name $regValueName
        if ($regValue.$regValueName -ne $regValueData) {
            Set-ItemProperty -Path $regSubkey -Name $regValueName -Value $regValueData -Type $regValueType
            Write-Output "[+] The registry value '$regValueName' in subkey '$regSubkey' has been updated to $regValueData."
        }
        else {
            Write-Output "[-] The registry value '$regValueName' in subkey '$regSubkey' already exists and is set to $regValueData."
        }
    }
    else {
        New-Item -Path $regSubkey -Force | Out-Null
        New-ItemProperty -Path $regSubkey -Name $regValueName -Value $regValueData -PropertyType $regValueType | Out-Null
        Write-Output "[+] The registry value '$regValueName' in subkey '$regSubkey' has been created and set to $regValueData."
    }
}

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Affected OS & Apps

Windows 11 22H2

Microsoft

Windows 10 22H2

Microsoft

Windows 10 21H2

Microsoft

Windows 11 22H2

Microsoft

Windows 10 22H2

Microsoft

Windows 10 21H2

Microsoft

Windows 10 1607

Microsoft

Windows 10 1507

Microsoft

Windows 10 1809

Microsoft

Windows Server 2022

Microsoft

Windows Server 2019

Microsoft

Windows Server 2016

Microsoft

Windows Server 2012

Microsoft

Windows Server 2008

Microsoft

Windows 11 21H2

Microsoft

Windows 10 20H2

Microsoft

Windows 10

Microsoft

Windows 7

Microsoft

Windows Server 20H2

Microsoft

Windows RT 8.1

Microsoft

Windows 8.1

Microsoft

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