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Account Takeover: My Near-Miss in Bug Hunting

How I Discovered an Account Takeover Vulnerability in a Cybersecurity Firm’s Website: A Story of Response Manipulation

account takeover

As a bug bounty hunter, I’m always eager to uncover hidden vulnerabilities in web applications. However, it’s not just about finding flaws for the sake of finding flaws—it's about understanding how they work and how they can be exploited. Today, I want to share with you how I uncovered a critical account takeover vulnerability on a cybersecurity firm’s website, all thanks to a simple but powerful technique known as response manipulation.

This vulnerability allowed an attacker to change the password of a user’s account without knowing the current password. Sounds pretty concerning, right? Let’s dive into how I stumbled upon this bug, and what impact it could have if left unchecked.

Cracking password



The Discovery: Testing a Password Reset Flow

It all began when I was testing the password reset functionality of a security firm’s website—let’s call it redacted.com. Most websites have a flow where you need to confirm your current password before resetting it. This is a basic security measure designed to prevent unauthorized users from changing your password without your consent.


But I’m no stranger to testing these flows. One of the first things I did was enter an incorrect password on the reset form, expecting the system to deny the request, as most systems would. However, this time, something felt off. Rather than seeing the expected error message and response, I decided to take a closer look using Burp Suite.

Burpsuite


With Burp Suite, I was able to intercept the HTTP requests and responses between my browser and the web application. This allowed me to dig deeper into how the password change flow was working behind the scenes.

The Key Insight: Intercepting and Manipulating the Response

What caught my attention was the response I received after submitting an invalid current password. The server returned a 401 Unauthorized status code, along with a response body like this:

code image server error


This seemed normal. The system was acknowledging that the password entered wasn’t correct, and that made sense.

But then I had an idea: What if I could somehow manipulate this response and bypass the password validation process?



I then intercepted a valid password change request (where the current password was correct and the request went through successfully) to compare the responses. This valid response looked like this:

code image server true



Now, I had two important pieces of information: one response indicated an error (when the password was wrong), and the other indicated a successful password change (when the password was correct).

This is where the exploitation came into play.



I could see that the response for a correct password was simply returning a "status": true in the response body with a 200 OK status code, while the error response for a wrong password returned "status": "error current password is incorrect" with a 401 Unauthorized.

The Exploit: Manipulating the Response to Change the Password

The next step was simple: I could now intercept the response when I tried to change the password with the wrong current password. Instead of accepting the “401 Unauthorized” response (which indicates the password was incorrect), I modified it to match the response I had intercepted for a successful password change—a 200 OK with the "status": true.



By changing the error response to a 200 OK with "status": true, I was essentially telling the system that the current password was valid, even though it wasn’t. This caused the system to proceed with the password change, bypassing the authentication check entirely.

At this point, the system believed that the request was legitimate and authorized, and my password was changed successfully without needing to know the current one.

The Impact: Account Takeover Potential

The real issue with this vulnerability is its potential for exploitation. Here’s how an attacker could take advantage of this flaw:

  1. Session Access: First, the attacker needs access to a victim's session. This could be done through techniques like session hijacking, phishing, or any other method that would give the attacker an active session.

  2. Interception: Once the attacker has access to the session, they could trigger the password reset flow, entering an incorrect current password on purpose.

  3. Response Manipulation: The attacker would then intercept the HTTP response, change the error response from the server (a “401 Unauthorized” error) to a success response (a “200 OK” with "status": true).

  4. Password Change: With the modified response, the system would think the current password was correct, allowing the attacker to change the account’s password without authentication.

This could lead to an account takeover, where the attacker gains control over the victim's account by simply changing the password, even without knowing the current password.

The Fix: Preventing Response Manipulation

This vulnerability highlights the importance of verifying current password authenticity before allowing any password changes. The fix for this vulnerability is fairly straightforward:

  • Proper Authentication Checks: The server should ensure that the user’s current password is correctly validated before allowing any password changes, regardless of any potential manipulation of responses.

  • Secure Response Handling: The server should avoid sending responses that can be easily manipulated to bypass authentication. Specifically, responses that indicate authentication failures should not allow an attacker to modify or bypass them.

The Takeaway: Always Test for Edge Cases

As a bug hunter, this experience was a reminder that even the most seemingly straightforward functionalities—like password resets—can harbor dangerous vulnerabilities if not tested thoroughly. It’s crucial to look at every angle, even the ones that seem obvious, because it’s often in these overlooked corners where security flaws hide.


I hope this blog serves as a reminder for developers and security professionals alike to always test and validate the most sensitive parts of a system, especially those that deal with authentication and account management. Whether you’re building an app or testing someone else's, don’t just assume the basics are secure—go beyond that and test for vulnerabilities that could potentially have serious consequences.


duplicate report



To the team at redacted.com, I’ve reported this vulnerability responsibly and guess what it was flagged as duplicate🤡. I hope this post has shed light on how response manipulation can lead to account takeovers and why it’s important to take extra precautions in password management systems.


Thanks for reading my blog, I hope you enjoyed your stay.



Happy Hunting🪲💻

Published on: Fri Feb 28 2025

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