Crypto bounty program got me $500 — Rate Limit Bypass

3 min readMay 6, 2024

Web3 security will be the future of bug bounty.

For a small bug on web3, you could got 2x comparing a medium or high severity bug on web.

The vulnerability is fixed so now, I can disclose the target. First response from the target[Kraken]-

Automatic Reply from The Company

Today I will tell you, how I secured $500 from a rate limit bypass.

How it started-

I was working as web pentester intern at a company. My boss gave me a target to hunt, unfortunately it was a public 😂 crypto program.

Initial Phase-

As you all know crypto targets are very secure and the chance of getting a bug is 0.000001% but something is better than nothing 🤫

I tried every possible way to find at least a single bug but nothing worked. I reported a bug called- password reset token not expiring after issuance of new one

But it got N/A 🤖

The Bug 🤑-

After trying several things I reached to the forgot password functionality to check for password reset poisoning but the functionality was safe from it.

I also checked for email triggering i.e., no rate limit on requesting password reset links.

But after every 5 attempts the account got locked for 3 minutes 🥴

I tried a simple bypass i.e., adding null characters after the email- e.g. \n \0 \x00 %0 etc., but nothing worked.

You should try all these.

The Bypass 😈-

After trying above bypasses, another bypass hit my mind- add a space after the email.

And ya that worked for me…😇

Steps to reproduce-

1. Intercept the forgot password request.

2. Send it to repeater, forward it, you will get the response that link to reset is sent ,forward it 4 times more, everything will be fine till here i.e., till now you received 5 password reset links in email. Now send one more time and you will be blocked for 3 minutes.

3. Now add a space after the email i.e.,

email=’ ‘ [see the space before the last quote in the email].

4. Send the above request 5 times, you will get 5 more links in the email and after that again you will be blocked.

5. Repeat step 3 i.e., add another space and in this way, adding a single space after every 5 attempts we have successfully bypassed the no rate limit.

Report ☠️-

I prepared a report and I haven’t used intruder for the POC. I just did what I showed you in steps to reproduce above. And after 3 days I got the email which I showed you above that I was awarded $500 and they assigned it low severity because a user can block these emails.


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Thanks for reading 🌹

#bugbounty #vulnerability #crypto #hacking