Cybersecurity researchers have uncovered a new technique where attackers use fake Captcha tests to trick people into installing malware called Lumma Stealer. This malicious program is designed to quietly search infected computers for valuable information, such as login credentials, cryptocurrency wallet details, and two-factor authentication codes.
The scheme first appeared on a Greek banking website, where users were shown what looked like a Captcha security test. Instead of a normal verification, the prompt instructed Windows users to copy a piece of text into their Run dialog box and press Enter. By doing so, victims unknowingly triggered the installation of Lumma Stealer without downloading a visible file.
According to data shared by DNSFilter, a security company monitoring the incident, clients came across this fake Captcha 23 times in just three days. Alarmingly, around 17% of users who saw it followed the instructions, which led to attempts to infect their systems with malware.
How Lumma Stealer Works
Once inside a computer, Lumma Stealer immediately begins searching for anything that can be exploited for profit. This includes saved browser passwords, cookies, stored two-factor authentication tokens, cryptocurrency wallets, and even the data kept in password managers. Cybercriminals can use this stolen information to commit identity theft, break into financial accounts, or steal digital assets such as crypto funds.
What makes this threat particularly concerning is that Lumma Stealer can be hidden on otherwise legitimate websites, meaning unsuspecting users may fall victim even without visiting suspicious or obviously harmful pages.
Malware-as-a-Service Model
Lumma Stealer is part of a growing cybercrime trend known as Malware-as-a-Service (MaaS). Under this model, professional malware developers create the malicious software, improve its ability to avoid detection, and maintain hosting services. They then rent access to the malware to other cybercriminals in exchange for subscription fees. This arrangement makes it easy for attackers with little technical expertise to launch damaging campaigns.
Earlier this year, authorities attempted to disrupt Lumma Stealer operations. The U.S. Department of Justice seized several domains linked to the malware, while Microsoft removed thousands of related websites. However, security analysts report that Lumma Stealer quickly resurfaced, showing just how resilient and profitable such services can be.
Part of Lumma Stealer’s popularity comes from its low cost. Subscriptions can be found on underground forums for only a few hundred dollars per month, yet the potential financial return for criminals is enormous. In recent analyses, experts estimated that hundreds of thousands of devices have been compromised, with losses reaching tens of millions of dollars.
The importance of staying alert online cannot be emphasised enough. Unusual instructions, such as copying text into a computer’s Run command should raise suspicion immediately. Cybersecurity specialists advise users to verify unexpected prompts and ensure their systems are protected with updated security tools to reduce the risk of infection.
In a recent multi-stage cyberattack, Cyble Research and Intelligence (CRIL) found an attack campaign hitting the manufacturing industry. The campaign depends upon process injection techniques aimed at delivering malicious payloads like Amaday Bot and Lumma Stealer.
Using a chain of evasive actions, the threat actor (TA) exploits diverse Windows tools and processes to escape standard security checks, which leads to persistent system control and potential data theft.
CRIL found an advanced multi-level attack campaign that starts with a spear-phishing mail. The email has a link that directs to an LNK file, hidden as a PDF file. When the fake PDF is clicked, it launches a series of commands. The LNK file is hosted on a WebDAV server, making it challenging for security software to trace.
“For instance, one of the malicious links observed in the campaign was hxxp://download-695-18112-001-webdav-logicaldoc[.]cdn-serveri4732-ns.shop. The attack’s effectiveness stems from its ability to exploit the name of a legitimate cloud-based document management system (LogicalDOC), commonly used in manufacturing and engineering industries, to convince targets into opening the file,” reports the Cyber Express.
After executing the LNK file, it opens ssh.exe, a genuine system utility that can escape security software checks. Via ssh.exe, a PowerShell command is activated to retrieve an extra payload via a remote server from mshta.exe.
Threat actors use this process to avoid detection via Google’s Accelerated Mobile Pages (AMP) framework merged with a compressed URL. The retrieved payload is a malicious script containing extra hacked commands that gradually deliver the last malicious payload to the target system.
Once the LNK file is executed, it launches ssh.exe, a legitimate system utility that can bypass security software’s detection. Through ssh.exe, a PowerShell command is triggered, which fetches an additional payload from a remote server using mshta.exe. This process is designed to evade detection by using Google’s Accelerated Mobile Pages (AMP) framework combined with a shortened URL.
The payload fetched is a script that contains additional obfuscated commands that eventually deliver the final malicious payload to the victim’s system.
CYBLE blog says, “The final payload, which involves the deployment of both Lumma stealer and Amadey bot, highlights the TA’s intent to steal sensitive information and maintain persistent control over compromised systems. Yara and Sigma rules to detect this campaign, are available for download from the linked GitHub repository.”
“We have identified more active malicious sites spreading the Lumma Stealer. It's important to note that while this technique is currently being used to distribute Lumma Stealer, it could potentially be leveraged to deliver any type of malicious malware to unsuspecting users,” say experts from Cloud SEK.
A CAPTCHA traditionally works as a security checkpoint, making sure that online activities are started by humans and not automated bots. However, hackers are misusing the CAPTCHA for malicious gains, creating a fake CAPTCHA challenge. When a user completes it, the CAPTCHA deploys a series of malicious commands.
The fake CAPTCHA tests ask request users to press a sequence that many users think is harmless. But, doing so starts the download and activation of a Power Shell script that installs the Lumma Stealer malware.
Cybersecurity experts from Palo Alto Networks believe Lumma Stealer is an information-stealing malware used for stealing data- passwords, cookies, and cryptocurrency wallet credentials. If the malware is present on a compromised device, it exposes users to major risks of financial fraud, cyberattacks, and identity theft.
The malicious CAPTCHA has massive scale distribution, experts at Hudson Rock noticed that if a user visits compromised websites, it automatically copies the malicious script to a user's clipboard. This can increase the chances of automatic triggering of an attack.
Additionally, experts have noticed an increase in this kind of attack, meaning cybercriminals are improving and implementing their attack tactics. These fake CAPTCHA tests can be spread via phishing emails and messages, which makes them a threat.
Check URLs: Make sure the site is authentic before interacting with any CAPTCHA.
Keep systems updated: Updated OS, browsers, and antivirus software can increase your security.
Stay cautious with CAPTCHA: Stay safe from any CAPTCHA test that requests any action beyond selecting images and text input.
Follow safe browsing hygiene: Do not click links or attachments from unknown messages or emails.