Top 3 Tools Used by Cyberattackers in 2020 and Early 2021

Three legitimate pentesting tools – PowerShell, Cobalt Strike, and PsExec – topped the list of tools used by cyberattackers in breaking into victims’ networks in 2020 and early 2021, according to Sophos’ report based from frontline threat hunters and incident responders.

In the report “The Active Adversary Playbook 2021,” Sophos found that PowerShell, followed by Cobalt Strike, and PsExec are the top 3 tools used by cyberattackers in 2020 and early 2021.

PowerShell, Cobalt Strike, and PsExec are legitimate tools used by IT administrators and security professionals for penetration testing, also known as pentesting – an authorized simulated cyberattack against an organization’s computer system to examine exploitable vulnerabilities. Threat actors, however, have been using these same pentesting tools to break into victims’ networks.

According to Sophos report, correlations emerge among the top 3 tools found in victims’ networks. The report added that when PowerShell is used in an attack, Cobalt Strike was seen in 58% of cases, and PsExec in 49% of cases; Cobalt Strike and PsExec were used together in 27% of attacks; and the combination of Cobalt Strike, PowerShell, and PsExec occurs in 12% of all attacks.

PowerShell

PowerShell is a task-based command-line shell and scripting language designed for system administration in the Windows operating system. Attackers use PowerShell to conduct a number of malicious activities, including executing malicious code, creating new tasks on remote machines, identifying configuration settings, pulling Active Directory information from the target environment, evading defenses, exfiltrating data, and executing other commands.

The malicious software called “Emotet” has used PowerShell to retrieve the malicious payload and download additional resources like Mimikatz – ranked fourth in the tools used by cyberattackers in 2020 and early 2021 in the Sophos report. Mimikatz is capable of obtaining plaintext Windows account logins and passwords.

PsExec

PsExec is a free Microsoft tool that is used by IT administrators to execute a program on another computer. This tool has been used by attackers to download or upload a file over a network share.

Cobalt Strike

Cobalt Strike is a commercially available pentesting tool that’s marketed as "adversary simulation software designed to execute targeted attacks and emulate the post-exploitation actions of advanced threat actors."

This commercial pentesting tool was developed by researcher Raphael Mudge in 2012. This tool was recently acquired by HelpSystems. In 2020, the source code of Cobalt Strike version 4.0 was leaked to the public. Adversaries often use the purchased and pirated/cracked versions of Cobalt Strike.

This tool is capable of executing a payload on a remote host with PowerShell and using PsExec to execute a payload on a remote host. Cobalt Strike’s Beacon is used to perform actions such as collecting information on process details, reaching out to the command-and-control server on an arbitrary and random interval, breaking large data sets into smaller chunks for exfiltration, and capturing screenshots.

Real-World Examples

The tools PowerShell and Cobalt Strike were used in the recently unraveled supply chain attack on SolarWinds.

In the SolarWinds supply chain attack, attackers compromised the code update of SolarWinds’s product Orion, which gave the attackers the opportunity to attack customers that applied the compromised SolarWinds Orion update. The SolarWinds supply chain attack victims include cybersecurity firm FireEye and Microsoft.

In the blog post "Raindrop: New Malware Discovered in SolarWinds Investigation," security researchers at Symantec reported that the malicious software (malware) called "Raindrop" enabled the delivery of Cobalt Strike into the victims’ networks. Security researchers at Symantec reported that in the victim’s computer where the Raindrop malware was found, it was observed that several days later, PowerShell commands were executed on that computer, attempting to execute further instances of Raindrop malware on additional computers in the organization.

The top 3 tools, PowerShell, Cobalt Strike, and PsExec, used by cyberattackers in 2020 and early 2021 were all used by the group behind the ransomware called “DoppelPaymer.” Similar to modern-day ransomware, DoppelPaymer encrypts victims’ files, locking these victims out from accessing their files, and demands from victims to pay ransom in exchange for the decryption tool that would unlock the encrypted files.

Similar to other modern ransomware, the group behind DoppelPaymer threatens victims with the publication of their stolen files on the data leak site as part of the ransomware’s extortion scheme. In DoppelPaymer ransomware, PowerShell, Cobalt Strike, PsExec, and Mimikatz – ranked fourth in the tools used by cyberattackers in 2020 and early 2021 in the Sophos report – were used to stealing credentials, moving laterally inside the network, and executing different commands.

In the blog post "Ransomware groups continue to target healthcare, critical services; here’s how to reduce risk," Microsoft 365 Defender Threat Intelligence Team said that defenders should pay attention to malicious “PowerShell, Cobalt Strike, and other penetration-testing tools that can allow attacks to blend in as benign red team activities.”

“Security teams can defend their organization by monitoring and investigating suspicious activity,” Sophos in the “The Active Adversary Playbook 2021” said. “The difference between benign and malicious is not always easy to spot. Technology in any environment, whether cyber or physical, can do a great deal but it is not enough by itself. Human experience and the ability to respond are a vital part of any security solution.”

Cybersecurity Best Practices Against DarkSide Ransomware

The ransomware called “Darkside” wreaked havoc lately, with Colonial Pipeline, which operates the largest fuel pipeline in the U.S., as its latest high-profile victim.

Colonial Pipeline became aware of the ransomware attack last May 7, forcing the company to shut down its operations. The company was able to restart its operations last May 12.

A report from Bloomberg showed that Colonial Pipeline paid within hours after the attack the group behind Darkside ransomware nearly $5 million. According to the Bloomberg report, once nearly $5 million was paid, the group behind Darkside ransomware gave the decryption tool for Colonial Pipeline to restore its disabled computer network.

The decryption tool, however, was so slow that the Colonial Pipeline continued using its own backups to help restore the system, the report said. 

What Is DarkSide Ransomware?

DarkSide ransomware is a ransomware-as-a-service (RaaS) in which the ransomware developers receive a share of the proceeds from the cybercriminal actors who deploy the ransomware, known as “affiliates.”

This ransomware was first observed in the wild in August 2020 and has been known to target high-revenue organizations. Similar to modern ransomware, DarkSide ransomware encrypts victims’ files and demands from victims ransom payment in exchange for the decryption tool that would unlock the encrypted files.

Aside from data encryption and decryption, DarkSide ransomware also carries out data exfiltration and threatening victims that non-payment of ransom could lead to the public exposure of stolen data. In addition, the group behind DarkSide ransomware is also willing to carry out a Distributed Denial of Service (DDoS) attack against victims.

Tactics Used by DarkSide Ransomware Attackers

Researchers at FireEye in the blog post “Shining a Light on DARKSIDE Ransomware Operations” and researchers at McAfee in the blog post “DarkSide Ransomware Victims Sold Short” found that the group behind the DarkSide ransomware employed the following tactics:

. Password Spraying Attack Against Corporate VPN

To gain initial access to their victim’s network, the group behind DarkSide ransomware used password spraying against corporate VPN. In password spraying, an attacker circumvents the account lock-out countermeasures by trying the same password across many accounts before trying another password.

. Exploitation of CVE-2021-20016

To gain initial access to their victim’s network, the attackers exploited CVE-2021-20016, a SQL-Injection vulnerability in the SonicWall product that allows a remote unauthenticated attacker to perform SQL query to access username password and other session-related information.

. Phishing Emails

To gain initial access to their victim’s network, the attackers also used phishing emails to deliver the SMOKEDHAM – a malicious software (malware) that supports keylogging, taking screenshots and executing arbitrary .NET commands.

. Exploitation of Remote Desktop Protocol (RDP) Vulnerabilities

To gain initial access to their victim’s network, the attackers also exploited RDP, a proprietary protocol developed by Microsoft that allows users the ability to connect to another computer over the internet. In the past few years, a handful of security vulnerabilities on RDP had been identified and patched. Many, however, fail to apply the latest RDP patch.

. Leveraging TeamViewer

To establish persistence within the victim environment, the attackers also leveraged TeamViewer – a legitimate software that allows access to computers and networks remotely.

. Leveraging Mimikatz

To gain more privileges on the victim’s network, the attackers also used Mimikatz for credential harvesting.

. Leveraging NGROK

To bypass firewalls and expose remote desktop service ports, like RDP and WinRM, to the open internet, the attackers used the publicly available NGROK. 

. Leveraging Cobalt Strike BEACON

To maintain a foothold on the victim’s network, the attackers used Cobalt Strike BEACON. Cobalt Strike is a commercially available penetration testing tool. The group behind Cobalt Strike describes BEACON as a tool to “egress a network over HTTP, HTTPS, or DNS.”

Cybersecurity Best Practices

Below are some of the cybersecurity best practices in order to reduce your organization’s vulnerability to ransomware such as DarkSide and reduce the risk of severe business degradation once impacted by ransomware:

Use multi-factor authentication as an added protection to the single-factor authentication: the traditional username and password combination.

Filter emails to prevent malicious executable files from reaching end users.

Filter network traffic to prevent inbound and outbound communications with known malicious IP addresses.

Keep all software up to date by applying the latest patches in a timely manner.

Protect RDP with strong passwords, multi-factor authentication, VPN other security protections.

Implement application allow listing, allowing the systems to execute only software programs that are known and permitted by the security policy.

It’s important to note that the tactics above-mentioned aren’t just used by the group behind DarkSide ransomware. The said tactics are widely used as well by ransomware groups and other malware operators. As such, the cybersecurity best practices above-mentioned also apply to other forms of attacks.

To date, the group behind the Darkside ransomware has gone dark, making it unclear whether the group has ceased, suspended operation, or has changed its operations or maneuvering an exit. Since March 13, all the dark websites used by the group behind Darkside are down. These sites were used by the group to communicate with the public.

Investigation Shows Ryuk Ransomware Attack Caused by Pirated Software, Lack of Network Protection

Sophos recently revealed that a cyberattack involving Ryuk ransomware targeting a European biomolecular research institute was caused by a pirated software and lack of network protection.

According to Sophos, its Rapid Response team was called in to respond to a Ryuk ransomware attack targeting a European biomolecular research institute – an organization that partners with local universities and works with students on various programs.

The Ryuk ransomware attack on the European biomolecular research institute, Sophos reported, costs the institute a week’s worth of vital research data, as even though the institute had backups, these backups weren’t up to date. The operation of the institute was also impacted since all computer and server files were required to be rebuilt before the data could be restored.

Initial Compromise

A review of logs and historical data available traced the initial compromise of the Ryuk ransomware attack on the European biomolecular research institute to the moment when one of the institute’s partners, an external university student, installed a pirated data visualization software on the said student’s laptop.

The investigating team found that the institute allowed people outside the organization to access its network, with partners such as university students allowed to access the institute’s network via remote Citrix sessions without the need for two-factor authentication using their own personal computers.

The investigating team found that the partner-student of the institute who installed the pirated software posted a question on an online research forum asking if anyone knew of a free alternative of the data visualization software, of which an original software costs hundreds of dollars a year. When the partner-student of the institute didn’t find a free version, a pirated version was used instead.

According to Sophos’ Rapid Response team, the pirated software was a pure malicious software (malware) that immediately triggered a security alert from Windows Defender. In order to install the pirated software, the partner-student of the institute disabled Windows Defender as well disabled Windows Security Firewall.

The installed pirated software-malware capabilities include logging keystrokes, stealing browser, cookies and clipboard data. The pirated software-malware also enabled the attackers to steal the student’s access credentials for the institute’s network.

According to Sophos’ Rapid Response team, 13 days after the installation of the pirated software-malware, a remote desktop protocol (RDP) connection was registered on the institute’s network using the student’s credentials, and 10 days after this connection was made the Ryuk ransomware was launched. The investigating team added that the institute’s RDP connection triggers the automatic installation of a printer driver, enabling users to print documents remotely.

“It is unlikely that the operators behind the ‘pirated software’ malware are the same as the ones who launched the Ryuk attack,” said Peter Mackenzie, manager of Rapid Response at Sophos. “The underground market for previously compromised networks offering attackers easy initial access is thriving, so we believe that the malware operators sold their access on to another attacker. The RDP connection could have been the access brokers testing their access.”

Cybersecurity Best Practices

The Ryuk ransomware attack that targeted the European biomolecular research institute is a hard-earned lesson for the community.

While the partner-student of the institute is clearly at fault for using pirated software, the said cyberattack exposed the institute’s network weaknesses. Here are some of the cybersecurity best practices in order to fortify your organization’s network against cyberattacks such as Ryuk ransomware attack:

• Use two factor-authentication as this is an added layer of security
• Enable Windows Defender as well Windows Security Firewall
• Keep backups up to date
• Practice Network Segmentation
• In network segmentation, your organization’s network is divided into sub-networks so that in case one sub-network is compromised, the other sub-networks won’t be affected.
• Implement Least Privilege Access
• The least privilege concept restricts access to your organization’s network to only those who are required to perform routine, legitimate activities.
• Secure Remote Desktop Protocol (RDP) Connection

RDP is a proprietary protocol developed by Microsoft that allows users the ability to connect to another computer over the internet. In the blog post "Cybercriminals Actively Exploiting RDP to Target Remote Organizations", McAfee Labs said that as a result of the COVID-19 restrictions, organizations wanting to maintain operational continuity have allowed their employees to access networks remotely via RDP with minimal security checks in place, giving cyber attackers easy access to these networks.

In the past few years, a handful of RDP security vulnerabilities have been identified and patched by Microsoft. Organizations that lagged behind in applying these RDP patches are vulnerable to attacks.

In the blog post “Data science for cybersecurity: A probabilistic time series model for detecting RDP inbound brute force attacks,” Microsoft said that RDPs that are not protected by strong passwords, multi-factor authentication, virtual private networks (VPNs), and other security protections are vulnerable to brute force attack – a type of cyberattack that uses the trial-and-error method in guessing the correct username and password combination.