Back in August 2017, Trustwave Spiderlabs reported a spam campaign that distributed a new Locky variant called "diablo" As predicted that incident was just a primer for a much bigger campaign and indeed just a few weeks later a new variant of Locky was launched that was called "Lukitus."
At first, you may wonder why Lukitus? It seems to be patterned after the name "Loki", the well-known trickster god of the Norse mythology that could change his shape and sex. It also makes sense that it is related to "Loki" since the Locky family has a good track record of using mythological god names with its variants. However, as we dig a little deeper, we find that "Lukitus" is a Finnish word which means locking, perfectly fitting for a crypto locker ransomware.
Since the first debut of the Lukitus variant the actual behavior of the binary payload really hasn't changed much, but what is more interesting is how it has changed how it gets into the victim's system. In this blog we will summarize what transpired throughout its one-month activity before Locky changed to its more recent variant called "ykcol" (which we will cover in a separate post).
The first incident of the Lukitus variants involves several spam templates using blank subject lines or even emails regarding CSI, voice messages or even a payment receipts. The messages have attachments that could either be compressed JS or VBScript files. These script files are obfuscated and basically function to download the Lukitus binaries.
We saw multiple spam templates that used multiple subject lines relating to an image file or a scanned file. Also, instead of using the ever-popular archive file format of ZIP and RAR, the spammers opted to use 7zip to compress the malicious VBScript downloader.
And aside from the image/graphics subject lines, the campaign also included spam with an outstanding invoice theme using an attached Word document. Once this document is executed it runs a malicious macro script that uses the XMLHTTP object to download the Lukitus binaries. The macro script is also responsible for executing the download binaries.
The spammers also tried to vary the type of attachment they sent out. When using the sample templates about images or photos, scans and documents it shifts to a JS downloader instead. In some cases, where a malicious Word document is attached, we also saw some variations on how it performs the download routine. The spammers used a macro script with a PowerShell that accessed the System.Net.WebClient which, in turn, downloaded the Lukitus binaries instead of directly accessing a XMLHTTP object.
The spammers also tried to spam emails regarding fake fax and voice messages with a compressed JS downloader in a RAR file.
At some point, the attackers strayed away from using the usual email with attachments. Instead, the email template used a URL link (purportedly a copy of an invoice) that would entice users to click and eventually lead to a VBScript downloader.
The campaign also used a more convincing email template that tried to spoof a SAGE subscription invoice. Clicking the URL link downloaded a RAR file with a compressed VBScript downloader inside.
Soon after, the attackers reverted back to emails with attachments using a payment invoice theme with a little twist. The attached JS downloader is using both XMLHTTP object and PowerShell method to download the Lukitus binary files.
The problem of using a Sage email template is that it will only target a small number of users who know the software company Sage. So the spammers take it up a notch and use a fake Dropbox notification and a spoofed invoice from the Microsoft Store. Like the previous Lukitus-based email templates, the fake Microsoft invoice used both the URL and an attachment to trick users to open the VBScript downloader from the compressed 7Zip file.
The real surprising thing here is when the VBScript code was analyzed. The variable names used are characters and scenes related to the popular HBO series – Game of Thrones. We can safely assume that whoever runs this spam campaign are also fans of the TV series.
From the very first incident of the Locky-diablo variant in August we have expected follow through campaigns and we have not been disappointed. The spammers have bombarded the email gateway with all sorts of spam using different email templates. Bogus emails regarding pictures/graphics, scanned documents, fake invoices and spoofed account verification of well-known companies are all used. Malicious Word documents with macro scripts and combinations of compressed JS or VBScript downloaders all appear to be in the game plan for this group of actors, who also seem to be followers of the TV series Game of Thrones.
These behaviors reveal a constantly evolving bag of tricks, where the campaigns change daily, yet deliver the same ultimate payload. However, underneath all the tricks are common themes that we monitor closely to determine how the spammers evolve their email structures, and to provide timely email protection for our customers.