Password Reset ATO Bug Bounty Story

A few days ago, I was working on a target on YesWeHack.
Ignoring their unusual policies for a moment, I managed to discover something serious - an Account Takeover (ATO) vulnerability through the password reset flow.
Let me break down the full scenario step by step because it’s actually a very interesting case study in real-world security testing 🧠

First Attempts That Didn’t Work​

At the beginning, I started testing the password reset functionality normally.
My first idea was simple:

• Try to generate a reset link
• Modify it so it resets another user’s account password

But that approach didn’t work.
Then I checked whether the reset links expire after a certain time.
Surprisingly, they didn’t seem to expire at all, which is already a security concern - but according to the platform policy, it wasn’t considered reportable.
So I kept digging.

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The Breakthrough Idea 💡​

After testing multiple scenarios, I focused on a more interesting idea.
I created two accounts:

• Account A
• Account B

Then I triggered password reset for both accounts at the same time.
What I noticed was unexpected.
The reset requests were almost identical - about 96% similarity.
Only a few small values (around 4 fields containing letters and numbers) were different.
That small detail turned out to be the key.

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Building a Wordlist Attack Scenario​

At this point, I started thinking like an attacker.
I wrote a simple script to generate a wordlist of all possible variations for those changing values.
Then I used Burp Suite Intruder to automate the testing process.

The idea was simple:

• Capture the reset request
• Intercept it
• Replace the dynamic value with different combinations
• Send multiple requests automatically

After running the attack for a while, something interesting happened 👀
The response length started changing for specific requests.
That difference indicated that I had successfully found a valid reset token.
And just like that…

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Happy ATO 🎯​

I was able to complete an Account Takeover scenario via password reset manipulation.

Reporting the Vulnerability​

After confirming everything, I reported the issue with full details and a video demonstration.
The next day, I received a response:

“Need more information”

At first, I thought I might have missed something.
But later, they even sent me an account from their side to test further as a professional validation step.
That was unexpected, but I continued testing anyway.

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Sudden Change in the Platform Behavior ⚠️​

While investigating further, I noticed something strange:
The entire password reset functionality was suddenly disabled on the platform.
Everything stopped working.
Of course, this is something I’ve seen before - especially when a vulnerability is classified as critical and under internal patching.

Later, I submitted another detailed report with:

• Full explanation
• Proof of concept video
• Timeline of discovery

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Why This Bug Was Serious​

This vulnerability falls under a critical security category because it involves:

• Password reset manipulation
• Token predictability or correlation
• Potential account takeover (ATO)
• Weak validation of reset logic

Even small weaknesses in password reset flows can lead to full account compromise if attackers automate the process properly.

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Key Security Lessons From This Case 🧠​

This scenario highlights a few important security insights:

1. Password Reset Flows Are High-Risk​

They are one of the most targeted attack surfaces in web applications.

2. Small Pattern Differences Matter​

Even a few predictable fields can be exploited for enumeration or brute-force attacks.

3. Automation Is Powerful​

Tools like Burp Suite Intruder can turn small inconsistencies into exploitable vulnerabilities.

4. Real Security Is in the Details​

Sometimes the biggest vulnerabilities come from logic flaws, not technical bugs.

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Final Thoughts​

Bug bounty hunting is not always about finding complex exploits.
Sometimes it’s about noticing small patterns that others ignore.
In this case, a simple observation in the reset password flow turned into a full Account Takeover scenario 🚀
And as always in security:
The smallest detail can break the entire system 💀