I’m excited to share some significant news with you today: I’ve made a noteworthy discovery regarding a complete account takeover through the password reset feature.
During my investigation, I uncovered a critical vulnerability within the password reset functionality of https://www.vulnerable.website.com/forgetPassword. Surprisingly, the password reset code is inadvertently disclosed in base64 encoded format within the response. What’s even more alarming is that each reset request yields the same link. To compound the issue, the password reset code aligns with the user’s Email ID alongside a random 6-digit code. This oversight presents a glaring opportunity for malicious actors to reset any user’s password through brute force, thereby gaining unauthorized access to their account.
Steps to Reproduce
The application reveals user information via error messages on the Password Reset, allowing for user enumeration.
Before proceeding, I created an account with my email address to assess the application’s functionalities and behavior. Through this, I discovered that the token is expired after 2 hour and the application sends the reset password URL to the user with a reset token encoded in base64.
The reset password URL sent to the user when requesting a forgotten password appears as follows:
As you can see, the token is encoded in Base64. Decode the code using a base64 decoder. The decoded base64 token contains the Email Address and 6-digit random data.
Thus, it’s evident that the application utilizes this method to send the reset password token to every user. By leveraging user enumeration to obtain a valid user email, one can initiate a password reset request. However, since the token includes email and 6 random digits that are unknown, brute force is required.
We can create a combination of 999999 possible combinations, resulting in a total of 999999 reset password tokens to be used as payload. Subsequently, a password reset request can be made using the victim’s email and brute force with the token payload, enabling us to crack the correct token and reset the victim’s password.
Remediation
This blog exposes a critical vulnerability in the password reset functionality of [invalid URL removed]. Here’s how to fix it:
1. Fix the Token Format
The current token format combines the user’s email with a random 6-digit code. This predictability allows brute-forcing.
Implement a secure, random token generation process. Ideally, tokens should be long, cryptographically secure strings with no relation to user information.
2. Eliminate Base64 Encoding
Transmitting the token in base64 encoding exposes it within the email content.
Never send sensitive information like reset tokens directly in emails. Instead, consider sending a unique link to the password reset page where the user can enter their email for verification. A new, secure token can be generated and used for password reset upon verification.
3. Implement Rate Limiting
The blog mentions the application allows unlimited password reset attempts. This facilitates brute-forcing.
Enforce a rate limit on password reset attempts. This restricts the number of attempts allowed within a specific timeframe, hindering automated brute-force attacks.
4. Consider Multi-Factor Authentication (MFA)
Even with a secure token format, adding MFA introduces an extra layer of security.
Implement MFA during password resets. This requires a secondary verification factor, like a code sent to the user’s phone, in addition to the reset token, making unauthorized access significantly harder.
5. Address User Enumeration
The blog mentions the application reveals usernames through error messages. This allows attackers to identify valid usernames for brute-forcing.
Implement robust error handling that doesn’t disclose user information. Generic error messages indicating an invalid email or username should suffice.
By implementing these recommendations, [invalid URL removed] can significantly improve the security of its password reset functionality and prevent account takeovers through brute-forcing.
Additionally, users of the website can further protect themselves by:
Choosing strong, unique passwords for their account.
Enabling MFA if available.
Being cautious of unexpected password reset emails and only clicking links from trusted sources.
Conclusion
The user invitation flaw exposed highlights a critical security concern: the potential for unauthorized password resets. By prioritizing robust security measures throughout the software development lifecycle, organizations can build applications that are resistant to such attacks.
The outlined remediation steps, including implementing multi-factor authentication, securing the password reset process, and enforcing stricter admin access controls, provide a roadmap for improved security.
Remember, a secure development process coupled with regular penetration testing is essential for safeguarding user data and building trust with your users.
FAQs
1. How can attackers enumerate valid users before brute‑forcing tokens?
By submitting reset requests and analyzing differences in response times or messages for example, “user not found” vs “reset sent” attackers identify valid accounts.
2. Why is base64 encoding insufficient for protecting reset tokens?
Base64 simply encodes data without securing it; when combined with predictable elements like email and short numeric codes, tokens become trivial to brute-force.
3. Can logging and alerts detect a brute-force token attack?
Yes, sudden spikes in failed token submissions should be flagged, but only if thresholds are monitored and alerted effectively in real time.
4. Why is adding MFA during password resets a game‑changer?
Even if a token is compromised, requiring an additional verification step (e.g., SMS, email, authenticator app) blocks unauthorized account takeovers.
5. Does shortening token expiry reduce brute‑force risk?
Yes, shorter lifetimes limit attacker windows, but expiry periods must balance usability too short and legitimate users may be locked out.
6. How can systems prevent user enumeration via reset endpoints?
By returning identical responses regardless of email validity and avoiding clear error messages like “email not registered.”
7. Are UUID tokens safer than numeric codes for reset flows?
Yes, UUID4 tokens offer high entropy (128 bits), making brute-force attacks practically infeasible compared to limited-digit codes.
8. What makes token reuse a security risk?
Tokens that can be reused before expiry allow replay attacks; single-use tokens mitigated by marking them consumed immediately upon use.
