Alert - Microsoft SMBv3 Critical Vulnerability

Number: AL20-007
Date: 13 March 2020

AUDIENCE

This Alert is intended for IT professionals and managers of notified organizations. Recipients of this information may redistribute it within their respective 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

On 10 March 2020 Microsoft released a security bulletin detailing a critical, remotely-exploitable 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. in the way that Microsoft server message block (SMBv3) handles certain requests. This vulnerability may allow a remote, unauthenticated actor to execute arbitrary code on vulnerable SMB servers and SMB clients.
Microsoft has assigned CVE-2020-0796 to this vulnerability and has released an out-of-band security patch to fix all affected products.

DETAILS

The Cyber Centre is aware of a remotely-exploitable vulnerability in the way that Microsoft server message block 3.1.1 (SMBv3) handles certain requests. The vulnerability may allow a remote, unauthenticated actor to execute arbitrary code on the target SMB server or SMB client.

The following products are affected:
• Windows 10 Version 1903 for 32-bit Systems;
• Windows 10 Version 1903 for ARM64-based Systems;
• Windows 10 Version 1903 for x64-based Systems;
• Windows 10 Version 1909 for 32-bit Systems;
• Windows 10 Version 1909 for ARM64-based Systems;
• Windows 10 Version 1909 for x64-based Systems;
• Windows Server, version 1903 (Server Core installation); and
• Windows Server, version 1909 (Server Core installation).

To exploit a vulnerable SMB server, an unauthenticated actor would need to send a specially crafted packet to the targeted system. To exploit a vulnerable SMB client, an actor would need to configure a malicious SMBv3 server and convince a user to connect to it.

As out-of-band patches for this vulnerability have just been released by Microsoft, the Cyber Centre recommends that system owners refer to the Mitigation section of this Alert to protect their networks.

MITIGATION

The Cyber Centre recommends that system owners of vulnerable systems immediately apply the out-of-band security patches from Microsoft:

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0796

It is further recommended that restrictions on inbound / outbound TCP port 445 SMB traffic be implemented at the network border firewall FirewallA security barrier placed between two networks that controls the amount and kinds of traffic that may pass between the two. This protects local system resources from being accessed from the outside. .

Servers that cannot be patched immediately for operational reasons should have SMBv3 compression disabled as a workaround in order to protect them from exploitation. Note that disabling SMBv3 compression does not protect vulnerable clients.

To avoid potential interruption of service, recommended workarounds and patches should be tested with client systems before being deployed in a production environment. Detailed workaround instructions are available on the Microsoft website:

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/adv200005

REFERENCES

10 March 2020 notice on the Microsoft website: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/adv200005

Microsoft security patch:

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0796

 

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.