Growing Threat of Ransomware Reinfection

Growing Threat of Ransomware Reinfection

Switzerland's cybersecurity body, the Reporting and Analysis Centre for Information Assurance (MELANI), has cautioned local SMEs and large organizations against paying ransomware attackers due to the risk of ransomware reinfection.

In a recent advisory to local organizations in Switzerland, MELANI said it’s aware of cases in Switzerland and abroad where the same organizations have been victims of ransomware attacks several times within a very short period of time. Ransomware is a type of malicious software (malware) that encrypts victims’ files and forces victims to pay ransom in exchange for the decryption keys that would unlock the encrypted files.

According to MELANI, even if a ransom is paid, there’s no guarantee that the ransomware attacker will decrypt the data. Switzerland's cybersecurity body also cautioned that even when ransom payment is made, leading to the decryption of the encrypted data, the underlying infection of some ransomware will remain active. “As a result, the attackers still have full access to the affected company's network and can, for example, reinstall ransomware,” MELANI said.

Emotet and TrickBot are two of the malware cited by Switzerland's cybersecurity body that could cause ransomware reinfection on victims’ computers even after ransom payment and after decryption.

In October 2019, the Canadian Centre for Cyber Security issued an alert to organizations in Canada about the 3-in-1 infection process involving 3 malware: Emotet, TrickBot and Ryuk. According to the Canadian Centre for Cyber Security, Emotet, TrickBot and Ryuk ransomware are part of the 3-stage infection process, with Emotet as the first malware downloaded, TrickBot as the second malware downloaded, and Ryuk ransomware as the last malware deployed against victims’ networks by an organized and prolific actor or group of actors.

Emotet

Emotet, first detected in 2014, is a malware that’s distributed through emails containing malicious links or attachments. Victims are tricked into clicking these malicious links or attachments as the group behind Emotet uses branding familiar to the recipients.

According to the US Cybersecurity and Infrastructure Security Agency, once Emotet is downloaded on the victim’s computer, this malware uses a credential enumerator in the form of a self-extracting RAR file. This credential enumerator, the US cybersecurity body said, containstwo components: a bypass component and a service component. The bypass component is used to find writable share drives using SMB or brute force (attempt to crack a password or username using a trial and error method) users’ accounts, including the administrator account.The service component, meanwhile, writes Emotet onto thecompromised computer’s disk.

SMB, short for Server Message Block, is a network protocol used by computers running Microsoft Windows that allows systems within the same network to share files. “Emotet’s access to SMB can result in the infection of entire domains (servers and clients),” US Cybersecurity and Infrastructure Security Agency said.

Once the attacker gains access on the victim’s network via Emotet, the Trickbot malware is then downloaded and distributed to the compromised systems.

Trickbot

Trickbot, first detected in 2016, is a malware that has similar capabilities as Emotet. Similar to Emotet, Trickbot can brute force users’ accounts and spread onto as many computers as possible using SMB.

Analysis of the Trickbot showed that this malware uses PowerShell Empire, a publicly available tool. Designed as a legitimate penetration testing tool in 2015, PowerShell Empire has become a favorite tool among the well-financed threat groups. 

PowerShell Empire allows an attacker to escalate privileges, harvest credentials, exfiltrate information, and move laterally across the victim’s network. PowerShell Empire is difficult to detect on a network using traditional antivirus software as it operates almost entirely in memory, and it also uses PowerShell, a legitimate application. Empire also allows an attacker to install Ryuk ransomware on high-value targets.

According to the Canadian Centre for Cyber Security, Trickbot’s capabilities allow it “to map out the network and give the malicious actor a better understanding of the target, including the value of the data.”

Ryuk Ransomware

Ryuk ransomware first appeared in 2018. On its own, this ransomware doesn’t have the ability to spread onto as many machines as possible within a network, hence the dependency on other malware such as Emotet and Trickbot.

“The Ryuk ransomware itself does not contain the ability to move laterally within a network, hence the reliance on access via a primary infection, but it does, however, have the ability to enumerate network shares and encrypt those it can access,” UK's National Cyber Security Centre said. “This, coupled with the ransomware’s use of anti-forensic recovery techniques (such as manipulating the virtual shadow copy), is a technique to make recovering from backups difficult.”

Preventive and Mitigating Measures Against Ransomware

Every so often malware programs such as Emotet, Trickbot and Ryuk are able to access victims’ networks as a result of ignoring basic cybersecurity measures. Here are some basic cybersecurity measures in order to protect your organization’s network against malware such as Emotet, Trickbot and Ryuk:

1. Keep all software update;

2. Secure with two-factor authentication all remote access points such as virtual private network (VPN) and remote desktop protocol (RDP);

3. Practice network segmentation;

4. Keep backups offline; and,

5. Test backups often.

In the case of Ryuk infection, it’s important to note that cleaning up the affected computers isn’t enough as these “cleaned” computers could still be reinfected as the associate malware used by Ryuk, Emotet and Trickbot, could be lurking on networked systems that were not initially affected by the ransomware.