CVE-2021-34527: Microsoft Windows Print Spooler Remote Code Execution Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, 124 days after the CVE record was published.

How likely is exploitation in the next 30 days?

99.8%

EPSS score, percentile 100 of all scored records

How severe?

8.8 High

CVSS v3.1 base score, given by the CNA

What should I do?

CISA deadline 3 May 2022. Apply updates per vendor instructions.

Advisories and patches (1)

Which versions are affected?

Affected

• from 10.0.10240.0 to before 10.0.10240.18969
• from 10.0.14393.0 to before 10.0.14393.4470
• from 10.0.17763.0 to before 10.0.17763.2029
• from 10.0.0 to before 10.0.17763.2029
• from 10.0.0 to before 10.0.19042.1083
• from 10.0.19044.0 to before 10.0.19044.1415

and 14 more in the table below

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 3 May 2022.

Advisories and patches

• Windows Print Spooler Remote Code Execution Vulnerability (Vendor advisory, Patch)

Linked from CISA's catalog entry

• https://www.cisa.gov/news-events/directives/ed-21-04-mitigate-windows-print-spooler-service-vulnerability
• https://nvd.nist.gov/vuln/detail/CVE-2021-34527

Affected products and versions

As listed in the CVE record.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

Microsoft Windows Print Spooler contains an unspecified vulnerability due to the Windows Print Spooler service improperly performing privileged file operations. Successful exploitation allows an attacker to perform remote code execution with SYSTEM privileges. The vulnerability is also known under the moniker of PrintNightmare.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2021-34527 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Nov 2021.
• CISA marks it as known to be used in ransomware campaigns.
• The due date CISA sets for the required action is 3 May 2022.
• The CVE record was published on 2 Jul 2021, 124 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 8.8 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 99.8% (percentile 100), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

Windows Print Spooler Remote Code Execution Vulnerability

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.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-269

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

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