How severe is CVE-2021-34527?

CVE-2021-34527 has a CVSS score of 8.8/10, rated HIGH. Immediate patching is strongly recommended.

Which products are affected by CVE-2021-34527?

CVE-2021-34527 affects the following products: microsoft windows 10 20h2, microsoft windows 10 21h2, microsoft windows 10 22h2, microsoft windows 10 1507, microsoft windows 10 1607, microsoft windows 10 1809, microsoft windows 11 21h2, microsoft windows 11 22h2, and 7 more.

How do I patch CVE-2021-34527?

Apply the microsoft windows 10 20h2 security patch or hotfix for CVE-2021-34527 on the affected version, following the vendor advisory for your exact build.

How do I detect CVE-2021-34527 across my infrastructure?

Inventory every microsoft windows 10 20h2 deployment and check each version against the affected-products list above.

How do I mitigate CVE-2021-34527 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Is CVE-2021-34527 actively exploited in the wild?

Yes. There are 23 known exploit references for CVE-2021-34527, including 16 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-34527?

CVE-2021-34527 has an EPSS (Exploit Prediction Scoring System) score of 99.8%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2021-34527 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-34527 (Microsoft Windows Print Spooler Remote Code Execution Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2022-05-03. The required action was: Apply updates per vendor instructions. This CVE has been used in known ransomware campaigns. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

Which products and versions are affected by CVE-2021-34527?

CVE-2021-34527 affects microsoft windows 10 20h2; microsoft windows 10 21h2; microsoft windows 10 22h2; microsoft windows 10 1507, and 11 more product(s). Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-34527 published, and has it been updated?

CVE-2021-34527 was published on July 2, 2021 and was last updated on August 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🛡️

CISA KEV · ACTIVELY EXPLOITED

HIGH severity

CVE-2021-34527 — Windows 10 20h2

HIGH

CVE-2021-34527 is a high-severity (CVSS 8.8) remote code execution vulnerability in microsoft windows 10 20h2. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) and has been used in ransomware campaigns — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.

A remote code execution vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability…

Published

Jul 2, 2021

Updated

Aug 10, 2026

Affected

15 products

Patched

See advisory

Exploits

23 known

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03 — including use in ransomware campaigns. Federal agencies were required to remediate by 2022-05-03.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-34527.

EPSS Exploitation Probability

via FIRST.org ↗

99.8%probability of exploitation in next 30 days

Very High Risk0.00%

Lower risk than most CVEs100th percentile — riskier than 100% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-34527 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.

Description

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.

Affected Products

15 products · 17 configurations

windows 10 20h2microsoft

< 10.0.19042.1083

range

windows 10 21h2microsoft

< 10.0.19044.1415

range

windows 10 22h2microsoft

< 10.0.19045.2251

range

windows 10 1507microsoft

< 10.0.10240.18969

range

windows 10 1607microsoft

< 10.0.14393.4470

range

windows 10 1809microsoft

< 10.0.17763.2029

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.