Some may know the term CAPTCHA (Completely Automated Public Turing tests to tell Computers and Humans Apart). Most won’t recognise the name but would probably recognise a CAPTCHA if they came across it. They can quite often be seen as a nuisance but they play an important role in security.
CAPTCHA has been a trusted security mechanism for blocking bots and automated attacks for some time. However, cybercriminals have weaponized this trust by creating fake CAPTCHA pages - a deceptive tactic used to steal credentials, distribute malware, and manipulate user behaviour.
Businesses falling victim to a fake CAPTCHA scheme can result in data breaches, financial loss, and reputational damage. This article explores how fake CAPTCHAs operate, their risks to businesses, and the best strategies to stay protected.
PROBLEM: How Fake CAPTCHA Pages Work
Cybercriminals design fake CAPTCHA pages to resemble legitimate verification processes, often very difficult to distinguish from the real thing. These fraudulent pages may appear in:
Spoofed business login portals. Attackers embed fake CAPTCHA forms on phishing sites impersonating company login pages.
Infected advertising networks (Malvertising). Malicious ads redirect users to fake CAPTCHAs before serving malware.
Social engineering attacks. Fake CAPTCHA prompts trick users into giving away credentials or clicking harmful links.
Once a user engages with a fake CAPTCHA, this may trigger automatic malware downloads that compromise business systems.
The Dangers of Fake CAPTCHA in more detail
Exploited CAPTCHA services
Many businesses integrate third-party CAPTCHA services into their websites, assuming they are secure. However, compromised CAPTCHA services can introduce malicious scripts that turn a genuine CAPTCHA into an exploitative one. Attackers can, for example, capture usernames, passwords, customer and financial details by installing keylogging software without the business realizing it.
Session Hijacking and Account Takeovers
Fake CAPTCHA pages are often used as a prelude to session hijacking. When an employee enters their credentials into a phishing CAPTCHA page, attackers can capture the session token, allowing them to bypass login requirements. On the one hand they can gain access to corporate applications and sensitive systems and on the other hand web users can be redirected to fraudulent login portals or scam websites.
Business Email Compromise (BEC) and Fraud
Once an attacker captures business login credentials via a fake CAPTCHA page, they can execute Business Email Compromise (BEC) scams. This allows them to:
· Send fraudulent invoices to customers and partners.
· Divert payroll funds to attacker-controlled accounts.
· Access and manipulate sensitive business communications.
Increased Spear-Phishing Attacks on Employees
A successful CAPTCHA phishing attack often results in more sophisticated spear-phishing campaigns targeting executives and employees. Attackers use compromised credentials to craft highly convincing internal emails, tricking staff into revealing further sensitive information or executing financial transactions.
SEO Poisoning and Brand Exploitation
Cybercriminals often manipulate search engine results (SEO poisoning) to rank fake CAPTCHA pages higher in searches related to businesses or their services. Unsuspecting employees or customers searching for login pages, IT support, or secure document portals may unknowingly click on malicious links, further exposing business systems.
SOLUTION: How Businesses Can Strengthen Their Defences
Implement Advanced Threat Detection
Standard firewalls and antivirus solutions may not detect fake CAPTCHA-based attacks. More effective methods are:
· AI-driven phishing detection that can analyse website behaviour rather than just URL reputation.
· Threat intelligence feeds that track emerging CAPTCHA scams and update security policies accordingly.
· Browser isolation technologies to prevent employees from interacting with untrusted scripts.
Secure Business Domains and Employee Portals
This reduces the chances of those fake business login pages being created:
· Domain-Based Message Authentication (DMARC), DKIM, and SPF to prevent attackers from spoofing your business email domain.
· Regularly monitor for typosquatting domains (e.g., "yourbusiness-login.com" instead of "yourbusiness.com").
· Ensure employee login portals use CAPTCHA solutions that support challenge-response verification, not just click-based validation.
Monitor for Credential Stuffing Attempts
Even if an attacker gains credentials via a fake CAPTCHA, businesses can still mitigate damage by:
· Using bot detection systems to flag suspicious login attempts.
· Implementing rate limiting on login pages to prevent brute-force attacks.
· Requiring hardware security keys or biometric authentication to prevent unauthorized access.
Leverage Dark Web Monitoring
Since attackers frequently sell stolen credentials, businesses should:
· Use dark web monitoring services to detect if employee or customer credentials appear on underground marketplaces.
· Enforce automated credential rotation for accounts that may have been compromised.
Conduct Red Team Exercises
Businesses should simulate real-world CAPTCHA phishing attacks to assess employee response and identify vulnerabilities in security protocols. Regular security awareness drills can significantly reduce employee susceptibility to these threats.
Case Study 1: Real-World CAPTCHA Phishing Attacks
Fake Google reCAPTCHA Used in Microsoft 365 Credential Theft (2021)
Security researchers discovered a phishing campaign in which attackers used fake Google reCAPTCHA pages to trick users into entering their Microsoft 365 credentials. Employees received phishing emails with voicemail attachments, leading them to a convincing CAPTCHA page before redirecting them to a fake Microsoft login portal.
Outcome:
Many corporate credentials were stolen.
Attackers used compromised accounts to send further phishing emails internally.
Businesses faced financial and reputational damage.
Case Study 2: Credential Phishing Campaign Exploiting Open Redirect Links
Another widespread phishing campaign abused open redirect links to deceive users. After completing a fake CAPTCHA, victims were directed to a counterfeit Microsoft Office 365 login page. Since the CAPTCHA gave an illusion of legitimacy, users were more likely to trust the fraudulent login page.
Outcome:
Stolen credentials enabled business email compromise (BEC) attacks.
Attackers gained unauthorized access to cloud services, leading to data breaches.
SYSTEM to maintain THE SOLUTION: always stay ahead of evolving CAPTCHA Threats
By investing in proactive security measures, conducting regular security awareness training, and implementing advanced detection mechanisms, businesses can indeed protect themselves and their customers from falling victim to these attacks.
Cybercriminals are constantly refining their tactics, but with the right defences in place, businesses can stay one step ahead.
Stay vigilant, stay secure!
Further Reading
Zscaler Report
Microsoft Security Blog
Imperva Article – What is CAPTCHA:https://www.imperva.com/learn/application-security/what-is-captcha/#:~:text=CAPTCHA%20stands%20for%20the%20Completely,but%20relatively%20easy%20for%20humans.
Regola article on the Importance of Employee Training:
Regola Article on Credential Stuffing Attacks:
Mimecast article on SPF, DKIM, and DMARC
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