Attackers are increasingly spreading malware using a unique method: a fake CAPTCHA as the initial infection vector. Researchers from multiple companies reported on this campaign in August and September. The attackers, who mainly targeted gamers, first transmitted the Lumma stealer to victims via websites hosting cracked games.
The recent adware research shows that this malicious CAPTCHA is spreading through a wide range of online resources unrelated to gaming, including adult sites, file-sharing services, betting platforms, anime resources, and web apps that monetise traffic. This shows that the distribution network is being expanded to reach a larger pool of victims. Furthermore, we discovered that the CAPTCHA distributes both Lumma and the Amadey Trojan.
Malicious CAPTCHA
It's critical to comprehend how the attackers and their distribution network function in order to prevent falling for their tricks. Legitimate, non-malicious offers are also included in the ad network that pushes pages with the malicious CAPTCHA.
It works as follows: the user is redirected to additional resources when they click anywhere on a page that uses the ad module. As is common with adware, the majority of redirects take users to websites that advertise security software, ad blockers, and similar products. Sometimes, though, the victim is directed to a page that contains the malicious CAPTCHA.
Unlike genuine CAPTCHAs, which are intended to safeguard websites from bots, this copycat promotes illicit resources. As with the previous stage, the victim does not always come across malware. For example, the CAPTCHA on one of the sites invites the visitor to scan a QR code, which leads to a betting site.
The Trojans are distributed using CAPTCHAs that provide instructions. By clicking the "I'm not a robot" button, you can copy the powershell line.exe -eC bQBzAGgAdABhA <...>MAIgA= to the clipboard and displays the following "verification steps":
- To open the Run dialogue box, use Win + R.
- Subsequently, paste the clipboard line into the text field using CTRL + V.
- Finally, press Enter to execute the code.
Payload: Amadey trojan
Researchers have discovered that the same effort is also propagating the Amadey Trojan. Since 2018, Amadey has been the subject of multiple security reports. In short, the Trojan downloads multiple modules that steal credentials from major browsers and Virtual Network Computing (VNC) systems.
It also detects cryptocurrency wallet addresses in the clipboard and replaces them with those owned by the attackers. One of the modules can also capture screenshots. In some cases, Amadey downloads the Remcos remote access tool to the victim's device, allowing the attackers complete control over it.
From September 22 to October 14, 2024, over 140,000 users encountered ad scripts. According to Kaspersky's telemetry data, more than 20,000 of these 140,000 users were routed to infected sites, where some encountered a phoney update notification or a fake CAPTCHA. Users from Brazil, Spain, Italy, and Russia were the most commonly affected.
