Alert - Ongoing Vulnerabilities Involving Windows Print Spooler - UPDATE 1

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

AUDIENCE

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

PURPOSE

An Alert is used to raise awareness of a recently identified cyber threat Cyber threatA threat actor, using the internet, who takes advantage of a known vulnerability in a product for the purposes of exploiting a network and the information the network carries. that may impact cyber information assets, and to provide additional detection DetectionThe monitoring and analyzing of system events in order to identify unauthorized attempts to access system resources. and mitigation advice to recipients. The Canadian Centre for Cyber Security Cyber securityThe protection of digital information, as well as the integrity of the infrastructure housing and transmitting digital information. More specifically, cyber security includes the body of technologies, processes, practices and response and mitigation measures designed to protect networks, computers, programs and data from attack, damage or unauthorized access so as to ensure confidentiality, integrity and availability. ("Cyber Centre") is also available to provide additional assistance regarding the content of this Alert to recipients as requested.

OVERVIEW

Microsoft has published a knowledge base article describing CVE-2021-36958 [1], a new local privilege escalation vulnerability VulnerabilityA flaw or weakness in the design or implementation of an information system or its environment that could be exploited to adversely affect an organization's assets or operations. 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.

DETAILS

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.

MITIGATION


UPDATE 1

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.

REFERENCES

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

[2] Cyber Centre Alert AL21-011

[3] Cyber Centre Alert AL21-015

[4] CERT/CC VU#131152

 

NOTE TO READERS

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 Critical infrastructureProcesses, systems, facilities, technologies, networks, assets, and services essential to the health, safety, security, or economic well-being of Canadians and the effective functioning of government. Critical infrastructure can be stand-alone or interconnected and interdependent within and across provinces, territories, and national borders. Disruptions of critical infrastructure could result in catastrophic loss of life, adverse economic effects, and significant harm to public confidence. , 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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