Alert - Ongoing Vulnerabilities Involving Windows Print Spooler - UPDATE 1

Number: AL21-016 UPDATE 1
Date: 12 August 2021
Updated: 15 September 2021


This Alert is intended for IT professionals and managers of notified organizations.


An Alert is used to raise awareness of a recently identified cyber threat that may impact cyber information assets, and to provide additional detection and mitigation advice to recipients. The Canadian Centre for Cyber Security ("Cyber Centre") is also available to provide additional assistance regarding the content of this Alert to recipients as requested.


Microsoft has published a knowledge base article describing CVE-2021-36958 [1], a new local privilege escalation vulnerability involving the Windows Print Spooler service. There is no patch available for this vulnerability at the time of this publication. Workarounds have been provided by Microsoft.


On 11 August 2021 Microsoft published a knowledge base article [1] describing CVE-2021-36958, a local privilege escalation vulnerability in which the Windows Print Spooler service improperly performs privileged file operations. An actor exploiting this vulnerability could run arbitrary code with SYSTEM privileges. The actor could then install programs; view, change, or delete data; or create new accounts with full user rights.

As reported in the Cyber Centre Alert AL21-011 [2] and the Cyber Centre Alert AL21-015 [3], the Windows Print Spooler has been the source of several recent vulnerabilities. CVE-2021-36958 is the latest addition to the PrintNightmare group of vulnerabilities.

There have been multiple names used in open-source channels to describe this current vulnerability before CVE-2021-36958 was provided, including “PrintNightmare v4” and “SystemNightmare”. Additionally, CERT/CC has published Vulnerability Note VU#131152 [4] to detail information about this vulnerability.

The Cyber Centre is aware that a proof of concept exists.



On 14 September 2021, a patch for CVE-2021-36958 was released as part of the September 2021 Security Updates [1].

There is currently no patch available for CVE-2021-36958. The workaround provided by Microsoft is to stop and disable the Print Spooler service [1]. This will impede the ability to print.
Windows updates have been published for the other vulnerabilities related to the Windows Print Spooler. Refer to the previously released Cyber Centre Alerts [2][3] for more information.


[1] Windows KB Article – CVE-2021-36958

[2] Cyber Centre Alert AL21-011

[3] Cyber Centre Alert AL21-015

[4] CERT/CC VU#131152



The Canadian Centre for Cyber Security (Cyber Centre) operates as part of the Communications Security Establishment. We are Canada's national authority on cyber security and we lead the government's response to cyber security events. As Canada's national computer security incident response team, the Cyber Centre works in close collaboration with government departments, critical infrastructure, Canadian businesses and international partners to prepare for, respond to, mitigate, and recover from cyber events. We do this by providing authoritative advice and support, and coordinating information sharing and incident response. The Cyber Centre is outward-facing, welcoming partnerships that help build a stronger, more resilient cyber space in Canada.


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