Threat Intelligence / CVE / CVE-2021-34527

CVE-2021-34527 — Microsoft Windows 10 1507

CISA KEVRansomware
CVSS v3.1 8.8 (HIGH) · EPSS 94.2% (higher than 99.9% of all scored CVEs) · Priority 10/10 · Published 2021-07-02

As of 2025-12-18, CVE-2021-34527 is a HIGH-severity vulnerability in Microsoft Windows 10 1507, CVSS v3.1 8.8, EPSS 94.2% (99.9th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), with a US federal remediation deadline of 2022-05-03, and CISA links it to known ransomware campaigns. Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2021-34527, most recently “Ransom Cartel ransomware creator Maksim Silnikau sentenced to 16 years in federal prison”.

Last updated: 2025-12-18

What is CVE-2021-34527?

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.

The record classifies CVE-2021-34527 under weakness class NVD-CWE-noinfo. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 19 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 1898 days ago.

Severity and exploitation probability

CVSS v3.1 base score
8.8 — HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS (FIRST)
94.2% probability of exploitation in the next 30 days, higher than 99.9% of all scored CVEs
CISA KEV
Listed since 2021-11-03, federal remediation deadline 2022-05-03 — used in known ransomware campaigns
Threadlinqs priority
10/10 — CISA lists it as used in ransomware, which Threadlinqs scores at the maximum
Published
2021-07-02, last modified 2025-12-18

Is CVE-2021-34527 being exploited?

CISA added CVE-2021-34527 to the Known Exploited Vulnerabilities catalog on 2021-11-03, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2022-05-03 under BOD 22-01. CISA flags the vulnerability as one used in known ransomware campaigns. It currently carries a trending score of 40 in the Threadlinqs vulnerability feed.

Affected products and versions

How to fix CVE-2021-34527

The record marks a vendor fix as available for CVE-2021-34527. Patch reference: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34527. Vendor advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34527. Because CVE-2021-34527 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2022-05-03. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2021-34527

2 tracked threats in the Threadlinqs corpus reference CVE-2021-34527, either in the campaign’s CVE list or as an indicator on the campaign record.

Sources

Seeded from nvd and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2021-34527 are available via the Threadlinqs MCP server (Purple tier). View plans →

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