Actively exploited in the wild
Microsoft Windows Print Spooler Remote Code Execution Vulnerability
Microsoft - Windows · Listed in the CISA KEV since 2021-11-03. This indicates confirmed attacks in production environments.
Required action: Apply updates per vendor instructions.
CVE-2021-34527
HighCVSS 8.8KEVExploitation Probability (EPSS)
Very high risk100th percentile - higher than 100% of all known CVEs
Summary
A remote code execution vulnerability exists in the Windows Print Spooler service due to improper privileged file operations. An attacker can exploit it to run arbitrary code with SYSTEM privileges, allowing them to install programs, modify data, or create accounts with full user rights. Microsoft has released security updates, but additional registry and Group Policy settings must be verified.
Risk Assessment
The risk to the organization is critical as an attacker can gain full control of the system, potentially leading to data theft, malware installation, or permanent damage to infrastructure. The vulnerability can be exploited remotely, increasing the attack surface.
Recommendation
Immediately install the security updates from the Security Updates table for your Windows system. Additionally, ensure that the registry keys NoWarningNoElevationOnInstall and UpdatePromptSettings are set to 0 or not defined, and that Point and Print Group Policy settings are correctly configured.
Original NVD description (English source)
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.