Summary
In January, Netskope Threat Labs observed a new malware campaign using fake CAPTCHAs to deliver Lumma Stealer. Lumma is a malware that works in the malware-as-a-service (MaaS) model and has existed since at least 2022. The campaign is global, with Netskope Threat Labs tracking victims targeted in Argentina, Colombia, the United States, the Philippines, and other countries around the world. The campaign also spans multiple industries, including healthcare, banking, and marketing, with the telecom industry having the highest number of organizations targeted.
Researchers have observed attackers delivering Lumma via multiple methods, including cracked software, the Discord CDN, and fake CAPTCHA pages. The payloads and techniques involved in the infection chain also vary, with the attackers employing techniques like process hollowing and PowerShell one-liners. In this recent campaign, Netskope identified new payloads being delivered, new websites employing malvertising, and the use of open source snippets to bypass security controls.
Key findings
- A new Lumma Stealer campaign using fake CAPTCHAs, multiple new websites employing malvertising, and multiple new payloads and evasion techniques targeting Windows users worldwide.
- The infection chain includes a step where the attacker asks the victim to execute a command from their clipboard using the Windows Run command, making it difficult to flag via technologies like browser-based defenses.
- One of the payloads contains a snippet based on an open-source tool for bypassing Windows Antimalware Scan Interface (AMSI), a step designed to evade malware protection capabilities.
Details

The infection chain typically begins when the victim visits a website that redirects them to a fake CAPTCHA page. Once the victim accesses the URL, a fake CAPTCHA is displayed, instructing the victim to perform a particular sequence of actions that leads to the execution of the next stage of the infection chain.
Lumma Stealer has been using a particular flavor of fake CAPTCHAs in its attack chain since August 2024 that instruct the victim to run commands on their computer to kick off the infection. The fake CAPTCHAs are an exceptionally creative piece of social engineering designed to trick the victim into downloading and executing malware outside the browser. Even users who are savvy enough to know not to download and run files on the web may not realize what they are doing when they follow the instructions in the CAPTCHA. Furthermore, downloading malware payloads outside the browser serves an anti-analysis mechanism, evading browser-based cybersecurity controls.
In the campaign currently targeting Netskope customers, the fake CAPTCHA presents instructions to open the Windows Run window by pressing Windows+R, pasting the clipboard’s content in the run window using CTRL+V, and then pressing ENTER to execute it. By doing so, the user executes a command that infects their machine. This specific sequence is essential for the successful execution of the next stage, and it only works in Windows environments.

Behind the scenes, the website code contains a JavaScript snippet that is responsible for adding a command to the clipboard. This command relies on the native mshta.exe Windows tool to download and execute an HTA file from a remote server. Using mshta is a classic example of LOLBIN, a technique often used by attackers to circumvent defenses by proxying malicious code execution via trusted binaries.
By downloading and executing malware in such ways, the attacker avoids browser-based defenses since the victim will perform all of the necessary steps outside of the browser context.

