CVE-2021-34527

Scores

EPSS

0.943high94.3%
0%20%40%60%80%100%

Percentile: 94.3%

CVSS

8.8high3.x
0246810

CVSS Score: 8.8/10

All CVSS Scores

CVSS 3.x
8.8

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS 2.0
9.0

Vector: AV:N/AC:L/Au:S/C:C/I:C/A:C

Description

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 then install programs; view, change, or delete data; or create new accounts with full user rights.

UPDATE July 7, 2021: The security update for Windows Server 2012, Windows Server 2016 and Windows 10, Version 1607 have been released. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability.

In addition to installing the updates, in order to secure your system, you must confirm that the following registry settings are set to 0 (zero) or are not defined (Note: These registry keys do not exist by default, and therefore are already at the secure setting.), also that your Group Policy setting are correct (see FAQ):

  • HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint
  • NoWarningNoElevationOnInstall = 0 (DWORD) or not defined (default setting)
  • UpdatePromptSettings = 0 (DWORD) or not defined (default setting)

Having NoWarningNoElevationOnInstall set to 1 makes your system vulnerable by design.

UPDATE July 6, 2021: Microsoft has completed the investigation and has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. See also KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates.

Note that the security updates released on and after July 6, 2021 contain protections for CVE-2021-1675 and the additional remote code execution exploit in the Windows Print Spooler service known as “PrintNightmare”, documented in CVE-2021-34527.

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Sources

msrcnvd

Related Vulnerabilities

Exploits

Exploit ID: CVE-2021-34527

Source: cisa

URL: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Recommendations

Source: nvd

Apply an updateMicrosoft has addressed this issue in the updates for CVE-2021-34527. Note that the Microsoft update for CVE-2021-34527 does not effectively prevent exploitation of systems where the Point and Print NoWarningNoElevationOnInstall is set to a non-0 value. Microsoft indicates that systems that have NoWarningNoElevationOnInstall is set to a non-0 value are vulnerable by design. For systems that do not have the CVE-2021-34527 installed, or have Point and Print configured insecurely, please consider the following workarounds:Apply a workaroundMicrosoft has listed several workarounds in their advisory for CVE-2021-34527. Specifically:Microsoft Option 1 - Stop and disable the Print Spooler serviceThis vulnerability can be mitigated by stopping and disabling the Print Spooler service in Windows.If disabling the Print Spooler service is appropriate for your enterprise, use the following PowerShell commands:Stop-Service -Name Spooler -ForceSet-Service -Name Spooler -StartupType DisabledImpact of workaround Disabling the Print Spooler service disables the ability to print both locally and remotely.Microsoft Option 2 - Disable inbound remote printing through Group PolicyDisable the “Allow Print Spooler to accept client connections:” policy to block remote attacks.Impact of workaround This policy will block the remote attack vector by preventing inbound remote printing operations. The system will no longer function as a print server, but local printing to a directly attached device will still be possible.Note: The Print Spooler service must be restarted for this workaround to be activated.Block RPC and SMB ports at the firewallLimited testing has shown that blocking both the RPC Endpoint Mapper (135/tcp) and SMB (139/tcp and 445/tcp) incoming traffic at a host-based firewall level can prevent remote exploitation of this vulnerability. Note that blocking these ports on a Windows system may prevent expected capabilities from functioning properly, especially on a system that functions as a server.Enable security prompts for Point and PrintEnsure that the Windows Point and Print Restrictions are set to Show warning and elevation prompt for both installing and updating drivers in the Windows Group Policy. Specifically the HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint\ key should have NoWarningNoElevationOnInstall and UpdatePromptSettings entries that are both set to 0.Restrict printer driver installation ability to administratorsAfter the Microsoft update for CVE-2021-34527 is installed, a registry value called RestrictDriverInstallationToAdministrators in the HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint\ key is checked, which is intended to restrict printer driver installation to only administrator users. Please see KB5005010 for more details.

URL: https://www.kb.cert.org/vuls/id/383432

Vulnerable Software (315)

Type: Configuration

Vendor: microsoft

Product: windows_10_1507

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_10_1607

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_10_1809

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_10_20h2

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_10_21h2

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_10_22h2

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_11_21h2

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_11_22h2

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_7

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd

Type: Configuration

Vendor: microsoft

Product: windows_8.1

Operating System: * * *

Trait:
{  "cpe_match": [    {      "cpe23uri": "cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*",      "versionEndExcluding": "10.0.10240.18969",      "vulnerable": true    },    {      "cpe23uri...

Source: nvd