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Authorities Warn of Active Global Campaign Leveraging Brute Force Technique
Authorities in multiple countries, including Canada, the US and the UK have warned of an ongoing global campaign leveraging brute force technique targeting enterprise and cloud environments.
Cybersecurity centers in the UK (National Cyber Security Centre), Canada (Canadian Centre for Cyber Security), and the US (National Security Agency, Cybersecurity and Infrastructure Security Agency, and Federal Bureau of Investigation) warned of the global brute force campaign that’s being carried out to gain access to enterprise and cloud environments of targeted organizations.
What Is Brute Force Attack?
Brute force is a type of cyberattack that uses the trial-and-error method in guessing the correct username and password combination.
Brute force is often used interchangeably with password spray. In the blog post "Protecting your organization against password spray attacks," Diana Kelley Cybersecurity Field CTO at Microsoft said that brute force is targeted, while password spray is the opposite.
In a brute force attack, a hacker goes after specific users and tries as many passwords as possible using either a full dictionary or one that’s edited to common passwords, Kelley said. In password spray, meanwhile, Kelley said a hacker acquires a list of accounts and attempts to sign into all of them using a small subset of the most popular, or most likely, passwords until a hit is made.
In a Joint Cybersecurity Advisory [PDF], UK’s National Cyber Security Centre and US security agencies (National Security Agency, Cybersecurity and Infrastructure Security Agency, and Federal Bureau of Investigation), said that since at least mid-2019 through early 2021, attackers used a Kubernetes cluster to conduct “widespread, distributed, and anonymized brute force access attempts” against hundreds of organizations worldwide. To hide the attacks’ true origin, the attackers’ Kubernetes cluster normally routes brute force authentication attempts through TOR and commercial VPN services, including CactusVPN, IPVanish, NordVPN, ProtonVPN, Surfshark, and WorldVPN.
Kubernetes is an open-source software that allows the deployment and management of containerized applications at scale. A Kubernetes cluster, meanwhile, contains a control plane and one or more compute machines or nodes.
According to the Joint Cybersecurity Advisory, what was being brute force attacked were organizations using Microsoft Office 365 cloud services, and targeted as well were other service providers and on-premises email servers using a variety of different protocols.
“This brute force capability allows the … actors to access protected data, including email, and identify valid account credentials,” the Joint Cybersecurity Advisory said. “Those credentials may then be used for a variety of purposes, including initial access, persistence, privilege escalation, and defense evasion.”
The Joint Cybersecurity Advisory said the attackers collected email from Office 365 using a compromised valid service account with elevated Privileges, and that the attackers used certutil.exe, a known "Living Off the Land" technique, to transfer a file into a target environment.
Exploitation of Known Vulnerabilities
The Joint Cybersecurity Advisory pointed out that once the attackers obtained credentials through brute force, various other known vulnerabilities were exploited by the attackers to gain further access and move laterally through the target network. Publicly known vulnerabilities such as CVE 2020-0688 and CVE 2020-17144 were exploited by the attackers.
CVE 2020-0688 is a remote code execution vulnerability in Microsoft Exchange Server. This vulnerability exists when the server fails to properly create unique keys at install time. “Knowledge of a validation key allows an authenticated user with a mailbox to pass arbitrary objects to be deserialized by the web application, which runs as SYSTEM,” Microsoft, in an advisory said.
CVE 2020-17144, meanwhile, is another remote code execution vulnerability in Microsoft Exchange. The vulnerability is caused by improper validation of cmdlet arguments.
The Joint Cybersecurity Advisory said that the exploitation of Microsoft Exchange servers occurred after valid credentials were identified through brute force campaign as these vulnerabilities CVE 2020-0688 and CVE 2020-17144 require authentication as a valid user.
Cybersecurity Best Practices
The Canadian Centre for Cyber Security, for its part, said it is highlighting the Joint Cybersecurity Advisory detailing the global brute force campaign to compromise enterprise and cloud environments as it’s important for system owners and operators responsible to defend their systems and networks from cyber threats.
Brute force attacks can be prevented or mitigated through the following cybersecurity best practices:
Microsoft’s security updates address the security vulnerabilities CVE 2020-0688 and CVE 2020-17144. It’s, therefore, important to keep all software, in this case, Microsoft Exchange, up to date to prevent further escalation of the malicious actors’ attack once they are able to break into your organization’s network through brute force campaign.
It’s also important to consider denying all inbound activity from known TOR nodes and other public VPN services to exchange servers or portals where this inbound activity isn’t associated with typical use.
Steve E. Driz, I.S.P., ITCP