Email OTP Bypass Using Kali Linux, Burp Suite, and Temp Mail – Ethical Hacking Demonstration

Explore how weak OTP implementations can be tested and bypassed in a legal, controlled environment using Kali Linux tools and Burp Suite. This educational guide is intended for ethical hackers and cybersecurity learners.

In this blog post, I will walk you through a step-by-step demonstration of an Email OTP (One-Time Password) bypass, conducted purely for educational and ethical testing purposes. The entire process was performed in a controlled environment using legal and publicly available tools and test websites. The goal is to raise awareness about the importance of secure OTP implementations and how weak setups can be vulnerable to brute-force techniques.

🧰 Tools & Resources Used

• Operating System: Kali Linux

• Proxy Tool: Burp Suite Community Edition

• Temporary Email Provider: Temp Mail

• Test Environment: Expand Testing – OTP Login Page

• Terminal Commands: Crunch, touch, cat

⚙️ Methodology

1. Accessed a Demo OTP Login Page
   Using the practice site at practice.expandtesting.com, I initiated an OTP login request by entering a disposable email address from Temp Mail.

2. Received the OTP via Temp Mail
   Once the OTP email arrived in my temporary inbox, I extracted the code provided for verification.

3. Generated a Numeric Wordlist with Crunch
   To simulate a brute-force attack, I used the crunch command in Kali Linux to create a list of all possible 6-digit numeric combinations:

   crunch 6 6 0123456789 -o /home/kali/Desktop/otpcode.txt
   

   This created a file with 1,000,000 combinations of 6-digit codes.

4. Verified OTP Presence in Wordlist
   After confirming that the correct OTP was indeed present within the generated file, I created a secondary file named otpcode2.txt, containing selected values including the correct OTP.

5. Used Burp Suite to Automate Testing
   With Burp Suite’s Intruder tool, I loaded otpcode2.txt as the payload and replayed the OTP verification request to analyze the response and identify successful code validation.

6. Successful Demonstration of Bypass
   By closely monitoring server responses and leveraging automation, I successfully demonstrated how OTP verification systems can be bypassed if not properly protected against brute-force attacks.

Key Takeaways

• OTPs are often considered a secure method of authentication, but poor implementation (e.g., no rate-limiting or lockouts) can make them vulnerable.

• Wordlist generation tools like Crunch, when paired with intercepting proxies like Burp Suite, can simulate real-world brute-force scenarios.

• Developers must implement rate-limiting, CAPTCHAs, IP blocking, and alerting mechanisms to secure OTP flows.

⚠️ Ethical Notice / Disclaimer

This post is for educational purposes only.
All demonstrations were carried out in a secure, ethical, and legal test environment.
I do not condone or encourage the use of these techniques on real systems or without proper authorization. Unauthorized hacking is illegal and punishable by law. Always follow ethical hacking principles and obtain permission before testing any system.

Cybersecurity professionals and enthusiasts should be aware of how simple oversights in authentication logic can lead to severe vulnerabilities. This demonstration is meant to educate and inspire developers, security researchers, and ethical hackers to build and maintain more secure systems.

If you found this post insightful, feel free to check out my YouTube channel for more ethical hacking tutorials and demos:

🔗 YouTube: @nmlletras

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