# Writeup for the challenge **_`Just Not My Type`_** from Killer Queen CTF 2021----
[ZeroDayTea]: https://twitter.com/ZeroDayTea
- ## Challenge Information:
| Name             | Category | Difficulty | Points | Dev        ||------------------|----------|------------|--------|------------|| Just Not My Type | Web      | Easy       | 248    |[ZeroDayTea]|
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# Description: I really don't think we're compatible
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# Solution:First thing i thought it was an sqli, but then i remembered they already gave us the source code for the challenge.
### Source-Code:
```php<h1>I just don't think we're compatible</h1>
<form method="POST">    Password    <input type="password" name="password">    <input type="submit"></form>```
The twist of the challenge is first we didn't have any link to the webapp, at first so the `$FLAG` variable is just a fake flag, so i look and nothing really wrong with the code but maybe the function `strcasecmp()` has some kind of vulnerability or not used in secure way, after googling a bit and reading the strcasecmp   php [Documentation](https://www.php.net/manual/en/function.strcasecmp.php)
Turns out that `strcasecmp()` is a single-byte function , after searching what that means and how to exploit it found that if you don't use it in a secure way it can leadto **Authentication Bypass** , the idea is to turn the password param into an empty array and the value to %22%22
Example: `http://vulntarget.com/type.php?password[]=%22%22`
and that gave me the flag :) 
![Pasted image 20211030045525](https://user-images.githubusercontent.com/33517160/139555131-39686fe2-8548-404a-a845-9aa5e97af02b.png)
## Flag: **`flag{no_way!_i_took_the_flag_out_of_the_source_before_giving_it_to_you_how_is_this_possible}`**