CVE-2021-34527 | Windows Print Spooler Remote Code Execution Vulnerability

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<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>

Published: 2021-07-02 Last update: 2025-12-18 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2021-34527 is rated Critical Active Threat (100/100): CVSS High severity, with high exploitation likelihood (EPSS 99.76%, 100th percentile). Core evidence: CISA KEV confirms active exploitation (added 2021-11-03) affecting Microsoft / Windows. Unauthenticated remote administrative access may be possible. EPSS rose +5.56% over the last day, indicating growing attacker interest. Mandatory action: The CISA remediation deadline has passed—treat as an emergency patch priority.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

CISA KEV Record for CVE-2021-34527

Name: Microsoft Windows Print Spooler Remote Code Execution Vulnerability · CISA KEV detail

Exploit added: 2021-11-03

Action due: 2022-05-03

Required action: Apply updates per vendor instructions.

Public exploit references (Exploit-DB) for CVE-2021-34527

EDB-ID Source Kind Published Link
nvd_ref exploit_tag Exploit-DB ↗
nvd_ref exploit_tag Exploit-DB ↗
nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-34527

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 94.20% 99.76% +5.56%
2 2026-03-15 94.27% 94.20% -0.07%
3 2025-12-28 94.27%

Full EPSS history (34 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34527

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.8 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
2.8 5.9 [email protected]
8.8 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
2.8 5.9 [email protected]
9.0 2.0 HIGH
AV:N/AC:L/Au:S/C:C/I:C/A:C Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:S)
A single authentication is required.
Confidentiality impact (C:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
8.0 10.0 [email protected]

Weakness enumeration for CVE-2021-34527

Affected software / configurations for CVE-2021-34527

Vendor Product Version Raw CPE
microsoft windows_10_1507 < 10.0.10240.18969 cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*
microsoft windows_10_1607 < 10.0.14393.4470 cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:*:*
microsoft windows_10_1809 < 10.0.17763.2029 cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:*:*
microsoft windows_10_20h2 < 10.0.19042.1083 cpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:*:*
microsoft windows_10_21h2 < 10.0.19044.1415 cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:*:*
microsoft windows_10_22h2 < 10.0.19045.2251 cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:*:*
microsoft windows_11_21h2 < 10.0.22000.318 cpe:2.3:o:microsoft:windows_11_21h2:*:*:*:*:*:*:*:*
microsoft windows_11_22h2 < 10.0.22621.674 cpe:2.3:o:microsoft:windows_11_22h2:*:*:*:*:*:*:*:*
microsoft windows_7 cpe:2.3:o:microsoft:windows_7:-:sp1:*:*:*:*:*:*
microsoft windows_8.1 cpe:2.3:o:microsoft:windows_8.1:-:*:*:*:*:*:*:*
microsoft windows_rt_8.1 cpe:2.3:o:microsoft:windows_rt_8.1:-:*:*:*:*:*:*:*
microsoft windows_server_2008 cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:*:*
microsoft windows_server_2008 r2 cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:*:*:*:*:x64:*
microsoft windows_server_2012 cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*
microsoft windows_server_2012 r2 cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*
microsoft windows_server_2016 < 10.0.14393.4470 cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*
microsoft windows_server_2019 < 10.0.17763.2029 cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*
microsoft windows_server_2022 < 10.0.20348.230 cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*
microsoft windows_server_20h2 < 10.0.19042.1083 cpe:2.3:o:microsoft:windows_server_20h2:*:*:*:*:*:*:*:*

References for CVE-2021-34527

cvelogic Threat Intelligence