One of the most ubiquitous security measures on the internet, CAPTCHA is not generally seen as a potential threat vector, but bad actors can leverage fake CAPTCHA pages to harvest sensitive information from their targets. Lumma Stealer, a malware that steals information, has recently begun leveraging fake CAPTCHA verification pages to lure and deceive users.
This malware is distributed as Malware-as-a-Service (MaaS), making it highly accessible for threat actors, but the attack chain is sophisticated, making it difficult to defend against. These novel attacks are alarming in their advanced methods and their level of deception, taking advantage of users’ innate trust to steal sensitive data.
Evolution of Attack Tactics: From Phishing to Fake CAPTCHA
Most individuals and organizations are wary of the threat of social engineering attacks, especially through common vectors like phishing emails. This has pushed threat actors to develop more convincing social engineering tactics and more sophisticated attacks to increase their success rate against modern security awareness.
Users overwhelmingly see CAPTCHA as a security measure rather than a potential threat vector. The involvement of a CAPTCHA verification inherently adds a layer of perceived legitimacy and security, which can cause the target to let their guard down and engage with these attacks. The manipulation of CAPTCHA pages for cybercriminal use is concerning as it highlights an area where many users are unprepared for potential risks to arise.
Inside the Attack Chain: How Lumma Stealer Works
Lumma Stealer begins the initial infection process by redirecting the target from a seemingly legitimate application or software to a fake CAPTCHA page. After clicking the “I’m not a robot” button, the CAPTCHA verification steps trigger a PowerShell command to execute, initiating the malware downloader to download onto the target device.
The technique of Lumma Stealer is complex and happens in multiple stages, making it difficult to detect and remove it from target devices. The initial payload is embedded in webpage code, with a further hidden payload being executed remotely via mshta.exe, a trusted Windows HTML running tool. This payload executes a JavaScript code, which reveals a PowerShell script, which downloads two .zip files and extracts the contents to execute the final Lumma Stealer payload.
The Lumma Stealer malware then uses a popular malware tactic known as process hollowing to avoid being detected. The malware injects a malicious payload into a legitimate program. All of these complexities make it difficult for security measures to detect and fight these threats.
Why Legitimate Software is Being Exploited
Attackers are motivated to target legitimate software in order to more effectively deceive and lure their targets. Exploiting legitimate software and public-facing applications enables attackers to take advantage of the trust that users place in them and redirect their targets to malicious pages. Users are not often primed to be wary of redirects in the process of a CAPTCHA test; they tend to assume that these pages are innately secure.
With bad actors taking advantage of this trust, the attack surface is broader than many have grown to expect. Rather than being solely a trustworthy security measure for protecting against bot attacks, CAPTCHA pages are now a prospective attack vector and other legitimate apps are likewise being abused for redirection in cyberattacks.
Advanced Deception and Persistence Tactics
The tactic of using fileless payloads in these social engineering attacks helps to improve the resilience of the malware, making it a persistent threat that is difficult to defend against. Security measures are not generally designed to detect or prevent these sophisticated attacks. The Lumma Stealer attacks use clipboard actions to their advantage, copying an encoded script that enables them to bypass traditional security tools and protocols.
“The Lumma Stealer campaign findings highlight significant trends that security teams must address,” says Sarah Jones, Cyber Threat Intelligence Research Analyst at Critical Start. The use of living-off-the-land techniques, multi-stage fileless attacks, “sophisticated obfuscation methods,” process hollowing and injection targeting legitimate applications, and the focus on cryptocurrency and password files are all factors that require organizations to take a new tack in defense.
Attacks using CAPTCHA and other novel techniques are likely to continue seeing increased usage, especially as MaaS makes it more convenient and efficient for threat actors to launch these attacks. “Expect more from adversaries related to CAPTCHA abuse, maturation of QR code phishing, and similar TTPs headed into 2025,” says Ken Dunham, Cyber Threat Director at Qualys Threat Research Unit.
Implications for Users and Organizations
These CAPTCHA attacks are representative of a number of trends of concern to organizations and individuals alike. Users face particular risks from the weaponization of trusted security mechanisms, as it conveys a sense of safety and opens up users to attacks. For an individual, falling victim to one of these attacks can result in compromised personal information, financial losses, identity theft, and other consequences. While the Lumma Stealer CAPTCHA campaign focused on cryptocurrency wallets and password files, tactics like this can be leveraged for a variety of criminal goals.
On an organizational level, these attacks can impact businesses, employees, and customers. The attack model and sophisticated tactics pose a danger to organizations as they leverage legitimate measures that many users frequently encounter and rarely question. The successful deployment of information-stealing malware like Lumma Stealer can lead to breaches of sensitive data, loss of revenue, regulatory penalties, and reputational damage for organizations.
Defensive Strategies: Combating CAPTCHA-Based Threats
Protecting against threats like this CAPTCHA social engineering campaign requires the implementation of advanced and proactive security measures. Employee cybersecurity awareness and training is essential for preventing social engineering attacks that prey on the human element. Attacks like this are often difficult for security tools to detect, but educating all users on the dangers of social engineering and fake CAPTCHA pages can go a long way toward protecting an organization.
Traditional security measures can fall short in the face of sophisticated social engineering attacks, so organizations are encouraged to implement advanced threat detection tools. Using strategies like real-time behavioral monitoring, PowerShell execution logging, and endpoint detection with the capability to detect fileless malware can help organizations protect against advanced threats.
Mitigating the risks of data exfiltration also relies heavily on robust security protocols to prevent unauthorized access to sensitive data. With the use of zero-trust principles, multi-factor authentication (MFA), anomaly detection, and other security and access controls, organizations can protect against the dangers of CAPTCHA-based threats.
The New Reality of Social Engineering Threats
The Lumma Stealer CAPTCHA attack method is highly deceptive, preying on users who put their trust in measures like CAPTCHA to ensure security. This campaign highlights the crucial need for organizations and individuals to update their understanding of security awareness to keep pace with modern threats. Organizations are encouraged to prioritize user security awareness training and invest in implementing advanced security tools designed to detect nuanced and sophisticated attacks.
With the popularity of MaaS providing a lower barrier for entry, complex and advanced attacks have become anyone’s game. Threat actors are constantly developing new tactics to increase the volume, efficiency, and efficacy of their attacks while evading known security measures. In this threat landscape, it is vital for organizations and users to exercise caution and vigilance to protect against innovative and evolving attacks.
