CVE-2021-34527: PrintNightmare
Improper Privilege Management: Is CVE-2021-34527 real, exploitable, or a false positive? Here's the community verdict.
signals
public sources
Confirmed exploited in the wild. Patch this first, regardless of the base score.
public exploits
links to sources — we don’t host codeA working exploit is publicly available from a maintained source. Treat this as higher urgency and verify your exposure.
baseline read
auto · not a community verdict
Real — exploited in the wild
CISA confirms active exploitation. Treat scanner hits as true positives unless your specific version or config is unaffected.
Based on CISA KEV
Confirm or dispute →CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
<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>
References
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Field notes & remediation
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- 0
Real and dangerous. It is a bug in the Windows Print Spooler service. An attacker (even a normal domain user) can run code as SYSTEM on a machine running the Print Spooler, both remotely and as a way to gain admin rights. Domain Controllers were a big worry because they run the spooler by default.
Who is affected: any Windows machine with the Print Spooler service enabled and reachable. The tricky part of this bug was the fix. The first patches were incomplete, and full protection also needed correct registry settings. Specifically, PointAndPrint NoWarningNoElevationOnInstall must not be set to 1.
To check: is the Print Spooler service running? Is the machine fully patched (August 2021 rollups and later)? Are the PointAndPrint registry values safe? If the spooler is running on a Domain Controller or a server that does not print, that is a red flag.
Commonly flagged by: Nessus, Qualys, Microsoft Defender.
- 0
Install the latest Windows cumulative updates (the August 2021 fixes and later). Then confirm the registry hardening. Under
HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint, NoWarningNoElevationOnInstall and UpdatePromptSettings must be 0 or absent. The strongest step is to disable the Print Spooler on any server that does not need to print, especially Domain Controllers:Stop-Service Spooler; Set-Service Spooler -StartupType Disabled.
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