We found in our honeypot a spam sample that delivers the info stealerLoki through an attached Windows Cabinet (CAB) file. The email that bears the malicious file poses as a quotation request to trick the user into executing the binary file inside the CAB file.
CAB is a compressed archive file format usually associated with various drivers, system files, and other Windows components installations.
The email has the header “REQUESTING QUOTATION,” seemingly coming from a client who is interested in availing the products and/or services offered by the receiver. The attachment supposedly contains the quotation request.
Figure 1. Sample email for Loki campaign
The CAB file attachment carries a binary file, which is a .NET compiled dropper that eventually executes Loki. The .NET dropper makes use of several layers of encrypted .NET modules that are then invoked.
Figure 2. Code snippet of .NET dropper
This will eventually lead to the execution of the Loki binary via process hollowing. Process hollowing is a malware technique that involves loading legitimate processes on the system and having it serve as a container for malicious code, thus remaining undetected. The technique was recently used by Monero Miner to evade detection.
Figure 3. Loki binary executed via process hollowing
Protection against info stealers and other malicious attachments
Attachments from malicious emails can serve as vehicles for info stealers such as Loki, other malware such as Ursnif, and even ransomware. Email-based threats can cost victims millions of dollars in damages, therefore it is important that employees are knowledgeable about email scams. Users can follow these best practices to avoid email threats:
Never download attachments or click links on emails from unfamiliar senders. This may lead to the installation of malware.
Be careful with sharing email addresses. Don’t share contact details on public web forums, social media, and other channels.
Be informed of the latest spam campaigns. Knowing the topics and contents of malicious emails can help avoid even those that use the most convincing social engineering techniques.
To supplement awareness and caution from users themselves, the following Trend Micro solutions are recommended: