Microsoft Windows up to Server 2019 Print Spooler Service spoolsv.exe RpcAddPrinterDriverEx dwFileCopyFlags PrintNightmare access control

Summaryinfo

A vulnerability labeled as critical has been found in Microsoft Windows. Affected is the function RpcAddPrinterDriverEx of the file spoolsv.exe of the component Print Spooler Service. Executing a manipulation of the argument dwFileCopyFlags can lead to access control. This vulnerability is registered as CVE-2021-34527. It is possible to launch the attack remotely. Furthermore, an exploit is available. Applying a patch is advised to resolve this issue.

Detailsinfo

A vulnerability has been found in Microsoft Windows (Operating System) and classified as critical. This vulnerability affects the function RpcAddPrinterDriverEx of the file spoolsv.exe of the component Print Spooler Service. The manipulation of the argument dwFileCopyFlags with an unknown input leads to a access control vulnerability. The CWE definition for the vulnerability is CWE-284. The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The weakness was published 07/01/2021 as VU#383432. The advisory is shared for download at kb.cert.org. The public release happened without coordination with the vendor. This vulnerability was named CVE-2021-34527. Technical details and also a public exploit are known. The MITRE ATT&CK project declares the attack technique as T1068.

It is possible to download the exploit at github.com. It is declared as attacked. As 0-day the estimated underground price was around $25k-$100k. This issue was added on 11/03/2021 to the CISA Known Exploited Vulnerabilities Catalog with a due date of 05/03/2022:

Apply updates per vendor instructions.

Applying a patch is able to eliminate this problem. It is possible to mitigate the problem by applying the configuration setting Stop-Service -Name Spooler -Force; Set-Service -Name Spooler -StartupType Disabled. The best possible mitigation is suggested to be patching the affected component.

The vulnerability is also documented in the vulnerability database at Zero-Day.cz (646). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Operating System

Vendor

• Microsoft

Name

• Windows

Version

• 7 SP1
• 8.1
• 10
• 10 20H2
• 10 21H1
• 10 1607
• 10 1809
• 10 1909
• 10 2004
• RT 8.1
• Server 20H2
• Server 1909
• Server 2004
• Server 2008 R2 SP1
• Server 2008 SP2
• Server 2012
• Server 2012 R2
• Server 2016
• Server 2019

License

• commercial

Website

• Vendor: https://www.microsoft.com/
• Product: https://www.microsoft.com/en-us/windows

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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