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Ransomware Targets SMBs via RDP Attacks

A series of ransomware attacks against small-to-medium companies are leveraging Remote Desktop Protocol (RDP) access to infect systems, Sophos reports.

A series of ransomware attacks against small-to-medium companies are leveraging Remote Desktop Protocol (RDP) access to infect systems, Sophos reports.

As part of these attacks, the mallicious actors abuse a commonly found issue in many business networks: weak passwords. After managing to crack and RDP password, attackers can easily install their malware onto the company’s systems with hopes to collect a ransom payment.

Discovering RDP ports exposed to the Internet isn’t difficult at all, Sophos explains. Cybercriminals can use specialized search engines such as Shodan for that and then abuse public or private tools to gain access to the discovered systems.

As part of the analyzed attacks, the actors used a tool called NLBrute to brute-force their way into the found systems by trying a variety of RDP passwords. Once they managed to find the right password, the attackers would immediately log into the network and create their own administrative accounts, Sophos says.

By doing so attackers can reconnect to the network even if the admin password they used for initial compromise has been changed. “They’ve already got backup accounts they can use to sneak back in later,” the researchers say.

Next, the attackers download and install low-level system tweaking software, such as Process Hacker, after which they turn off or reconfigure anti-malware applications. They also attempt to elevate privileges through abusing known vulnerabilities, including the CVE-2017-0213 and CVE-2016-0099 flaws that have been long patched by Microsoft.

The attackers also turn off database services to allow their malware to target databases, and also turn off the Windows live backup service called Volume Shadow Copy and delete existing backups, to prevent victims from restoring targeted files without paying. Next, they upload and run their ransomware.

According to Sophos, the attackers demanded a 1 Bitcoin ransom from their victims. Although numerous companies were hit, the attackers’ Bitcoin wallet shows a single transaction matching the demanded amount. Either victims have not paid, or they managed to negotiate lower payments, the security researchers say.

“The victims of this kind of attack are almost always small-to-medium companies: the largest business in our investigation had 120 staff, but most had 30 or fewer,” Sophos says.

To stay protected, organizations are advised to turn off RDP, or to protect it well if they need to use it regularly. They should also consider using a Virtual Private Network (VPN) for connections from outside their network, along with two-factor authentication (2FA), as well as to install available patches fast, to ensure their systems remain protected.

“You’ve probably heard the saying that ‘if you want a job done properly, do it yourself’. Sadly, there’s a niche of cybercrooks who have taken that advice to heart: if you’ve been sloppy setting up remote access to your network, they log in themselves and infect you with ransomware by simply running it directly, just like you or I might load Word or Notepad. This means the cyber criminals don’t need to mess around with emails, social engineering or malicious attachments,” said Paul Ducklin, Senior Technologist, Sophos.

The use of RDP to spread ransomware, however, isn’t a new practice. In fact, this attack method was so popular in the beginning of this year that it even topped email for ransomware distribution.

Last month, a BTCware ransomware variant called Payday was observed abusing the same method for infection. Security researchers investigating the attacks discovered that the malware operators were using brute-force attacks to crack RDP passwords and compromise the poorly secured systems.

Related: RDP Tops Email for Ransomware Distribution: Report

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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