Over the past few months, cyberattacks involving Netwalker ransomware have been steadily increasing and Netwalker has now become one of the biggest ransomware threats of 2020.
Netwalker ransomware is the new name for a ransomware variant called Mailto, which first appeared a year ago in August 2019. The threat actors behind the ransomware rebranded their malware as Netwalker in late 2019 and in 2020 started advertising for affiliates to distribute the ransomware under the ransomware-as-a-service model. In contrast to many RaaS offerings, the threat group is being particularly choosy about who they recruit to distribute the ransomware and has been attempting to build a select group of affiliates with the ability to conduct network attacks on enterprises that have the means to pay large ransoms and the data to warrant such large payments if attacked.
Netwalker ransomware was used in an attack in February on Toll Group, an Australian logistics and transportation company, which caused widespread disruption although the firm claims not to have paid the ransom. Like several other ransomware gangs, the Netwalker gang took advantage of the COVID-19 pandemic and was using COVID-19 lures in phishing emails to spread the ransomware payload via a malicious email attachment, opting for a Visual Basic Scripting (.vbs) loader attachments.
Then followed attacks on Michigan State University and Columbia College of Chicago, with the frequency of attacks increasing in June. The University of California San Francisco, which was conducting research into COVID-19, was attacked and had little choice other than to pay the $1.14 million ransom demand to regain access to essential research data that was encrypted in the attack. More recently Lorien Health Services, a Maryland operator of assisted living facilities, also had files encrypted by the Netwalker gang.
The recent attacks have seen the attack vector change, suggesting the attacks have been the work of affiliates and the recruitment campaign has worked. Recent attacks have seen a range of techniques used in attacks, including brute force attacks on RDP servers, exploitation of vulnerabilities in unpatched VPN systems such as Pulse Secure VPNs that have not had the patch applied to correct the CVE-2019-11510 vulnerability. Attacks have also been performed exploiting user interface components of web apps, such as the Telerik UI vulnerability CVE-2019-18935, in addition to vulnerabilities in Oracle WebLogic and Apache Tomcat servers.
With the ransoms paid so far, the group is now far better funded and appears to have skilled affiliates working at distributing the ransomware. Netwalker has now become one of the biggest ransomware threats and has joined the ranks of Ryuk and Sodinokibi. Like those threat groups, data is stolen prior to file encryption and threats are issued to publish or sell the data if the ransom is not paid.
The increase in activity and skill of the group at gaining access to enterprise networks prompted the FBI to issue a flash alert warning of the risk of attack in late July. The group appears to be targeting government organizations, educational institutions, healthcare providers and entities involved in COVID-19 research, and the attacks are showing no sign of slowing, in fact they are more than likely to increase.
Defending against the attacks requires a defense in depth approach and adoption of good cyber hygiene. An advanced spam filtering solution should be used to block email attacks, end users should be taught how to recognize malicious emails and shown what to do if a suspicious email is received. Vulnerabilities in software are being exploited so prompt patching is essential. All devices should be running the latest software versions.
Antivirus and anti-malware software should be used on all devices and kept up to date, and policies requiring strong passwords to be implemented should be enforced to prevent brute force tactics from succeeding. Patched VPNs should be used for remote access, two-factor authentication should be implemented, web filters used for secure browsing of the internet, and backups should be performed regularly. Backups should be stored on a non-networked device that is not accessible over the internet to ensure they too are not encrypted in an attack.