# What is CVE-2021-34527? > CVE-2021-34527 is a high-severity flaw (CVSS 8.8) in Windows Server 2012 from Microsoft, published on 2 July 2021. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at over 99%. If you run an affected version, patch it first. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-34527 ## At a glance - **Verdict:** Fix this now. Attackers are using this flaw today. If you run an affected version, it goes to the top of your list. - **Precursor Intelligence risk score:** 87 out of 100 (Critical); action: Emergency patch. Kept up to date as the evidence changes. - **Severity:** High (CVSS 8.8 out of 10) - **Known to be exploited:** Yes, it is on the government list of flaws known to be exploited - **Chance of use in the next 30 days:** over 99% (latest exploit-likelihood forecast) - **Published:** 2 July 2021 - **Record last updated:** 17 April 2025 - **Main product:** Windows Server 2012 from Microsoft - **Affected products:** 17 ## What is CVE-2021-34527? In plain terms It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline. ### The official 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. ### What kind of flaw is it? - Unknown: Unknown ### How an attack on it works - Where an attacker can be: Anywhere on the internet - How hard it is to pull off: Easy: no special conditions - Login needed first: An ordinary user account - Does someone have to click: No, nobody has to do anything - What an attacker gets: Can read data, change data and take it offline Severity vector: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H` ## Is CVE-2021-34527 being exploited? Yes Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%. Exploit likelihood over the last 7 days: >99%, >99%, >99%, >99%, >99%, >99%, >99%. ### Timeline - 2 July 2021: Published - 17 April 2025: Record last updated ### How Precursor Intelligence ranks it CVE-2021-34527 scores **87 out of 100 (Critical)**, with the action "Emergency patch". Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less: - Evidence it is being exploited: biggest factor - How severe it is: strong factor - How widely exposed it is: smaller factor - Threat activity around it: smaller factor 85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it. ## Who is affected by CVE-2021-34527? The published record lists 17 products. Versions are as published: "before 10.0.10240.18969" means every version up to, but not including, 10.0.10240.18969. - [Windows Server 2012](https://www.precursorintelligence.com/product/microsoft/windows_server_2012) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): r2 - [Windows 10 1507](https://www.precursorintelligence.com/product/microsoft/windows_10_1507) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.10240.18969 - [Windows 10 1607](https://www.precursorintelligence.com/product/microsoft/windows_10_1607) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.14393.4470 - [Windows 10 1809](https://www.precursorintelligence.com/product/microsoft/windows_10_1809) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.17763.2029 - [Windows 10 20H2](https://www.precursorintelligence.com/product/microsoft/windows_10_20h2) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.19042.1083 - [Windows 10 21H2](https://www.precursorintelligence.com/product/microsoft/windows_10_21h2) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.19044.1415 - [Windows 10 22H2](https://www.precursorintelligence.com/product/microsoft/windows_10_22h2) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.19045.2251 - [Windows 11 21H2](https://www.precursorintelligence.com/product/microsoft/windows_11_21h2) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.22000.318 - [Windows 11 22H2](https://www.precursorintelligence.com/product/microsoft/windows_11_22h2) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.22621.674 - [Windows 7](https://www.precursorintelligence.com/product/microsoft/windows_7) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): version not specified - [Windows 8.1](https://www.precursorintelligence.com/product/microsoft/windows_8.1) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): version not specified - [Windows Rt 8.1](https://www.precursorintelligence.com/product/microsoft/windows_rt_8.1) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): version not specified - [Windows Server 2008](https://www.precursorintelligence.com/product/microsoft/windows_server_2008) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): r2-sp1 - [Windows Server 2016](https://www.precursorintelligence.com/product/microsoft/windows_server_2016) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.14393.4470 - [Windows Server 2019](https://www.precursorintelligence.com/product/microsoft/windows_server_2019) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.17763.2029 - [Windows Server 2022](https://www.precursorintelligence.com/product/microsoft/windows_server_2022) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.20348.230 - [Windows Server 20H2](https://www.precursorintelligence.com/product/microsoft/windows_server_20h2) by [Microsoft](https://www.precursorintelligence.com/vendors/microsoft) (Operating system): before 10.0.19042.1083 ## How do I fix CVE-2021-34527? 1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list. 2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisory first in the list. 3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in. 4. **Check it wasn’t used before you patched.** Because criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance. ### References - [portal.msrc.microsoft.com](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34527) (Mitigation, Patch, Vendor advisory) - [packetstormsecurity.com](http://packetstormsecurity.com/files/167261/Print-Spooler-Remote-DLL-Injection.html) (Exploit, Third-party advisory, Vulnerability database) - [vicarius.io](https://www.vicarius.io/vsociety/posts/cve-2021-34527-printnightmare-detection-script) (Exploit, Third-party advisory) - [vicarius.io](https://www.vicarius.io/vsociety/posts/cve-2021-34527-printnightmare-mitigation-script) (Exploit, Third-party advisory) ## Questions ### What is CVE-2021-34527? CVE-2021-34527 is a high-severity flaw in Windows Server 2012 from Microsoft, published on 2 July 2021. It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline. ### How serious is CVE-2021-34527? It scores 8.8 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-34527 is 87 out of 100, which is Critical. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list. ### Is CVE-2021-34527 being exploited? Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%. ### Which versions does CVE-2021-34527 affect? For Windows Server 2012 from Microsoft: r2. The record lists 17 products in all, each with its versions, under "Who is affected" on this page. ### How do I fix CVE-2021-34527? Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. Because criminals are already using it, also check affected systems for signs of a break-in. ## Does CVE-2021-34527 affect you? Precursor Intelligence keeps checking for you: - **Tell us what you run.** Pick your software from a list, or let us work it out from your website. - **We match it to every flaw.** Over 400,000 published flaws, checked against your list. - **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it. - **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools. 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