Why are website captchas vulnerable to cyberattacks?

CAPTCHA and reCAPTCHA are common on all websites that require user interaction and the filling of online forms. Although they were a bit annoying at first, as CAPTCHA technology evolved into the Google reCAPTCHA standard, they became less numerous.

The question on the table is, however, how safe are they? Can they be fooled? For many years, CAPTCHAs have been the first line of defense against spambots, fake traffic, and denial of service (DoS) attacks. Most businesses and organizations with a significant online presence these days, when threat actors successfully circumvent CAPTCHA checks, they can seriously damage the credibility of online marketing campaigns and the reputation of those organizations.

What is CAPTCHA?

In the 1950s, computer scientist Alan Turning developed a test in which a computer was challenged to exhibit human characteristics through written communication. This test laid the foundation for future computer scientists to develop and use this conceptual methodology to create the CAPTCHA.


CAPTCHA (Completely Automated Turing test to tell Computers and Humans Apart) was designed to challenge users on web forms and authentication. Malicious actors create automated applications to fill out forms and click buttons on high-speed websites. This can lead to increased costs for organizations, wasted time and budget for their sales teams.

Due to the effectiveness of this challenge response in blocking malicious spambots, CAPTCHA quickly became the preferred method for effectively dealing with spambots.

CAPTCHA generates a distorted image from the source code and presents the image to the user as a visual challenge. The user would then analyze the image and respond to the prompt by providing a plain text qualifier.

CAPTCHA vulnerabilities

What is concerning, however, is that CAPTCHA could be bypassed and become useless when exploited by malicious actors.

Click on Farms

Much like click farms, threat actors can employ real people to gain access to websites they wish to target with spam. These farms usually consist of numerous workstations or mobile devices operated by malicious actors that interact with an organization’s website to capture nonsense information. As they are real human beings, they can decipher CAPTCHAS normally.

Cross-site scripting

Using a mechanism called Cross-site scripting, hackers could gain access to your customers’ personal information. Cross-site scripting (XSS) is an attack in which a malicious script is injected into the code of a trusted website. An XSS attack is frequently initiated by sending a malicious link to a user and tricking the user into clicking it.

If the application or website does not clean its data properly, the malicious script executes the threat actor’s code on the user’s system. Therefore, the attacker can steal the active session cookie from the user and, in this case, the CAPTCHA. This type of attack can easily occur without the knowledge of the user.

Optical character recognition software

By using modern Optical Character Recognition (OCR), hackers can solve most CAPTCHA challenges presented by your website. At the start of CAPTCHA, OCR technology was not yet advanced enough to decipher the mangled text used by the challenge. In recent years, OCR technology has advanced so much that cloud-based OCR robots can easily decipher distorted text.

Because CAPTCHAs offer multiple attempts for users to complete the challenge, threat actors can run their OCR software through CAPTCHA challenges multiple times before being denied access.

Artificial intelligence engines

Some malicious actors even go so far as to resort to artificial intelligence (IA) engines. These artificial intelligence engines rely on neural models, learning to decipher CAPTCHAs as they are exposed to them.

In conclusion

While modern reCAPTCHAs use much more complex mechanisms than simply presenting a challenge to a user, many websites still haven’t upgraded to the latest technology. The Google engine behind this technology would use biometric data such as mouse movements, browser history and IP addresses to interactively check whether the “person” using the website is a human or a bot.

Businesses and organizations need to understand that threat actors become extremely cunning and that cybersecurity systems need multiple layers of security to be effective. A comprehensive security platform will help organizations detect and block malicious traffic in real time, whether the source is paid or natural, and provide greater insight into marketing analytics.

To learn more about how click farms and bots bypass CAPTCHAs and how to stop them, visit this page.

Comments are closed.