Email Verification Bypass: A Rare Vulnerability

~ Dixith Kumar, Dec 25, 2024

Cyber Security Blogs >> Secrets In Code >> Email Verification Bypass
Introduction
Steps to Reproduce
Impact
Recommendations
Conclusion

Introduction

Authentication mechanisms form the backbone of secure web applications, ensuring that users accessing the system are legitimate. One common and effective method is email verification, which adds an additional layer of security by validating the ownership of an email address before granting access to critical functionalities. This mechanism is widely used to prevent unauthorized access, mitigate spam, and ensure accountability of users.

Despite its significance, flaws in the implementation of email verification can lead to severe vulnerabilities. In this write-up, I will share a rare instance of email verification bypass that I recently discovered. While such cases are uncommon, they underscore the importance of meticulous testing and secure development practices.

Target: A Crypto Website (Referred to as “example.com”)

Steps to Reproduce:

Steps to reprouduce are as follows:

  1. Create an account on the website.
  2. After account creation, a verification code is sent to the registered email address.
  3. I initially tested common attack vectors such as:
    • Rate limiting.
    • Host header injection.
    • Parameter pollution.
    • None of these approaches were successful.
  4. During further exploration, I noticed an option allowing users to change their email address for account verification.
  5. I clicked on the option to change the email and selected “Verify Later.”
  6. Upon returning to the dashboard, I observed that the email status was marked as “Verified,” despite not completing the verification process for the newly entered email.

I created a Proof of Concept (PoC) to demonstrate the vulnerability and reported it to the company. The issue was promptly acknowledged and resolved, earning me a valuable bounty.

Impact

Exploiting this vulnerability allows an attacker to:

  • Create an account using a victim’s email address.
  • Bypass the verification process, enabling unauthorized access.
  • Potentially use the victim’s email to perform malicious activities without their knowledge, such as phishing or fraudulent transactions.
Recommendations

To prevent such vulnerabilities, consider the following measures:

  1. Conduct a Threat Model Review:
    • Evaluate the design and architecture of the email verification functionality.
    • Identify potential abuse cases and ensure appropriate safeguards are in place.
  2. Implement Secure Development Practices:
    • Ensure email verification status is updated only after successful validation.
    • Use server-side checks to enforce verification logic and prevent tampering.
  3. Perform Thorough Penetration Testing:
    • Focus on manual abuse-case scenarios that automated tools might overlook.
    • Validate all edge cases and scenarios involving email changes and verification workflows.
  4. Enable Logging and Monitoring:
    • Monitor email verification attempts and flag unusual patterns for further investigation.
    • Ensure logs are detailed enough to trace back any suspicious activities.
  5. Implement Rate Limiting:
    • Limit the number of email change requests and verification attempts to mitigate abuse.
  6. Continuous Security Assessments:
    • Regularly assess the application for misconfigurations and vulnerabilities, especially in authentication workflows.

Conclusion:

This case highlights the criticality of secure email verification and the importance of a robust approach to application security. By rigorously testing and auditing functionalities, organizations can uncover and address such vulnerabilities before they are exploited.