There are many ways that ransomware can be downloaded onto business networks, but most commonly, ransomware attacks occur via Remote Desktop Protocol (RDP), drive-by downloads, or email.

RDP Attacks

Scans are performed to discover organizations with open RDP ports, which are then attacked using brute force tactics to guess weak passwords. Cybercriminals also add credentials from historic data breaches to their password lists.

The best way to defense against this method of ransomware delivery is to disable RDP entirely; however, RDP is often required for remote management or remote access to virtual desktops, so this may not be an option. If RDP cannot be disabled, there are steps that should be taken to make it as secure as possible.

Use of strong passwords is important to protect against brute force attempts to guess passwords. You should follow NIST advice on creating complex passwords. Passwords must be unique and not used on any other platform. Two-factor authentication should be implemented to prevent stolen credentials from being used.

You must make sure you are running the latest software versions for servers and clients. RDP connections to listening RDP ports should only be permitted through a secure VPN, and ideally, an RDP gateway should be used. You should also restrict who is permitted to login to remote desktop. Finally, you should use rate limiting to lock users out after a set number of failed attempts to enter the correct password.

Drive-By Ransomware Downloads

Drive-by downloads occur on websites controlled by hackers, either their own sites or insecure sites that have been compromised. Malicious scripts are added to the websites that download ransomware and other malware payloads onto a user’s device when they visit the malicious webpage. This method of attack does not require any user interaction, other than visiting the malicious website. That could occur by clicking a malicious link in an email, via a redirect, or even through general web browsing.

A web filter such as WebTitan is one of the best defenses against drive-by ransomware downloads. WebTitan is a DNS filtering solution that prevents end users from visiting websites known to be malicious. Rather than connecting to the website, the user will be directed to a local block page if they attempt to visit a known malicious website. WebTitan can also be configured to block downloads of risky file types such as executable files.

Email-Based Attacks

Ransomware is also commonly delivered via email. This could be via an embedded hyperlink to a website where a drive-by download occurs or via malicious scripts in file attachments. Protecting against email-based attacks requires a defense in depth approach, as no single solution will provide total protection against all email attacks.

An advanced email security solution such as SpamTitan should be implemented. SpamTitan scans all inbound and outbound emails and uses a variety of techniques, including machine learning, to identify and block potentially malicious emails. SpamTitan incorporates two antivirus engines that detect known malware variants and a sandbox to analyze suspicious files for malicious actions. Sandboxing protects against never-before-seen malware and ransomware variants.

End user training is also important to ensure that in the event of a malicious email reaching an end user’s inbox, it can be recognized as such. A web filtering solution will help to ensure that any attempt to visit a malicious website via a hyperlink in an email or email attachment is blocked before ransomware is downloaded.

Ransomware as a Secondary Payload

Several ransomware operators use commodity malware to deliver their ransomware payloads. The threat actors behind DoppelPaymer ransomware have been using the Dridex banking Trojan to deliver their malicious payload, while the Ryuk ransomware gang uses the TrickBot Trojan.

Even if these commodity malware infections are discovered and removed, the ransomware gangs may still have access to systems. These commodity malware infections are often viewed as relatively trivial and when these malware variants are discovered the attacks are not properly investigated. The Trojans are removed, but the ransomware operators continue to spread laterally before deploying their ransomware payloads.

In the case of TrickBot, once it is downloaded it gets to work harvesting data such as passwords files, cookies, and other sensitive information. Once the attackers have harvested all the data they can, a reverse shell is opened to the Ryuk ransomware operators who perform recon of the network and attempt to gain administrator credentials. They then use PSExec and other Windows tools to deploy ransomware on all devices connected to the network.

That is exactly what happened with the attack on the e-discovery firm, Epiq Global. The initial TrickBot infection occurred in December 2019. Access was provided to the Ryuk operators who deployed the ransomware on February 29, 2020. Prior to the deployment of ransomware, the Ryuk operators compromised computers in all 80 of Epiq’s global offices.

TrickBot and other Trojans are primarily delivered via phishing emails. SpamTitan will help to keep you protected against these Trojans and other ransomware downloaders.