CVE-2021-34527 PoC — Windows Print Spooler Remote Code Execution Vulnerability

Title:Windows Print Spooler Remote Code Execution Vulnerability (CVE-2021-34527)
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 then install programs; view, change, or delete data; or create new accounts with full user rights.</p> <p>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.</p> <p>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 (<strong>Note</strong>: 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):</p> <ul> <li>HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint</li> <li>NoWarningNoElevationOnInstall = 0 (DWORD) or not defined (default setting)</li> <li>UpdatePromptSettings = 0 (DWORD) or not defined (default setting)</li> </ul> <p><strong>Having NoWarningNoElevationOnInstall set to 1 makes your system vulnerable by design.</strong></p> <p>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 <a href="https://support.microsoft.com/topic/31b91c02-05bc-4ada-a7ea-183b129578a7">KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates</a>.</p> <p>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.</p>

Mitigation for CVE-2021-34527 RCE by setting WRITE ACLs

# CVE-2021-34527_mitigation
 Mitigation for CVE-2021-34527 RCE by setting WRITE ACLs.
 
These scripts are both to add and remove CVE-2021-34527(PrintNightmare) ACL mitigations that I wrote with assistance from /u/AforAnonymous from the reddit thread by Huntress in /r/MSP. I've personally tested this using a vulnerable Windows 1909 Host. Implementing the ACL mitigation caused PrintNightmare at https://github.com/cube0x0/CVE-2021-1675 to kick the error DCERPC Runtime Error: code: 0x5 - rpc_s_access_denied. Please note that while the github I just referenced states CVE-2021-1675, it is actually for CVE-2021-34527. Once the ACL was removed with the rollback script, PrintNightmare was again successful. 


This was inspired by https://blog.truesec.com/2021/06/30/fix-for-printnightmare-cve-2021-1675-exploit-to-keep-your-print-servers-running-while-a-patch-is-not-available/ and is not meant to be anything more than a potentially helpful mitigation until a patch is released. 

Note you may not be able to add new printers/drivers with the mitigation in place. If you need to add a new printer/driver, you can run the rollback script, add the new printer/driver, and then re-run the mitigation script. 

 [4.0K]  /data/pocs/d9e0e608cfcafaf0547332a0efe459ee54e46228
├── [ 804]  CVE-2021-34527_ACL_Mitigation.ps1
├── [ 735]  CVE-2021-34527_ACL_Mitigation_Rollback.ps1
└── [1.2K]  README.md

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