Source: Charles Walker Collection via Alamy Stock Photo

Hundreds of companies worldwide have been targeted with spear-phishing emails claiming copyright infringement that actually deliver an infostealer.

Starting in July, Check Point Research began to track the emails as they spread across the Americas, Europe, and Southeast Asia, coming from a new domain each time. Hundreds of its customers have been targeted, indicating that the real reach of the campaign may be far greater still.

The goal of the emails is to bait guilt-riddled victims into downloading Rhadamanthys, a sophisticated infostealer equally capable of pilfering nation-state intelligence or, in this case, cryptocurrency wallet passphrases.

CopyR(ight)hadamantys

No two emails in the campaign that researchers have dubbed "CopyR(ight)hadamantys" come from the same address, indicating that there must be some kind of automation behind their distribution. This automation proves awkward in some circumstances — like when an Israeli target receives an email almost entirely in Korean — and limits the emails' ability to realistically impersonate known brands.

Each one is made to seem as if it came from legal representatives of specific, known companies. Nearly 70% of those companies come from either technology — like Check Point itself — or from media and entertainment industries.

The profile of impersonated brands weaves in neatly with the story the attackers peddle: that recipients have posted some sort of content on social media that violated a copyright. "I assume everyone has done it to some degree in his life," says Sergey Shykevich, threat intelligence group manager at Check Point. "It just makes people hesitate and think, 'Oh, did I use some wrong image? Did I copy some text [by accident]?' Even if you didn't."

Recipients are asked to remove specific images and videos, the details of which are contained in a password-protected file. The file is actually a link that redirects the user to download an archive from Dropbox or Discord. The archive contains a decoy document, a legitimate executable, and a malicious dynamic link library (DLL) containing the Rhadamanthys stealer.

What to Know About Rhadamanthys

Rhadamanthys is a popular and accomplished information stealer. As Shykevich explains, "It's without any doubt the most sophisticated of those infostealers which are sold as commodity malware in the Dark Web. It's more expensive than other infostealers: Mostly you'll rent other infostealers from between $100 to $200. Rhadamanthys is more, around $1,000. It's much more modular, more obfuscated, and more complicated in how it's built: The way it loads itself, hides itself, all this makes detection much more complicated."

Among other features, the newest Rhadamanthys version 0.7 sports a slightly archaic machine-learning-based optical character recognition (OCR) component. It's hardly advanced artificial intelligence (AI) — it struggles with text in mixed colors, can't read handwriting, and only interprets the most popular fonts. Nonetheless, it helps the malware read data from static documents (like PDFs) and images.

In CopyR(ight)hadamantys, the OCR module comes loaded with a dictionary of 2,048 words associated with Bitcoin wallet protection codes. This might suggest that the attackers are after cryptocurrencies, which, if true, would also align with the campaign's broad targeting, characteristic of financially motivated campaigns. In recent months, Rhadamanthys has also been associated with nation-state threat actors like Iran's Void Manticore, and the pro-Palestine group "Handala."

One Strange Stealth Feature

Organizations looking to defend against CopyR(ight)hadamantys should start with phishing protections, but there's another quirk of the campaign worth noting as well.

After making landfall, the malicious DLL writes a significantly larger version of itself to the victim computer's Documents folder, which masquerades as a component of Firefox. This version of the file is functionally equivalent to the first. What makes it so much heavier is an "overlay" — useless data that serves two meta-functions. First, it changes the file's hash value, a common means by which antivirus programs identify malware.

Some antivirus programs also avoid scanning extra large files. "For example, they don't want to run files associated with games, with a huge number of gigabytes, because it makes for an intense load," Shykevich explains. By this logic, an otherwise uselessly larger Rhadamanthys file might improve its chances of avoiding detection. Though, he adds, "It's not extremely common because it's also not convenient for the attackers to deal with huge files. With some email solutions, you can't attach files more than 20MB, so you need to send the victim to some external resource. So it's a tactic, but it's not some crazy tactic that always works."

Organizations might want to sniff out at any particularly large files that employees may be downloading from emails. "It's not easy, because there are many reasons why some legitimate files will be big," he says. "But I think it's possible to implement some [effective] rules for what you can download."