Secure Image Upload Script

Introduction

Securing image uploads is crucial to prevent malicious activities and ensure the integrity of your website. This article provides a comprehensive solution to implement a secure image upload script that addresses various potential vulnerabilities.

Main Requirements

Building a secure image upload script involves several key requirements:

• File Type Validation: Prevent uploads of malicious file types (e.g., PHP scripts).
• Content Verification: Ensure uploaded images comply with image requirements (e.g., using GD library).
• Folder Isolation: Store images in a non-public location to prevent direct access.
• Server-Side Redirection: Display and retrieve images securely from the server.
• Local File Inclusion Prevention: Protect against vulnerabilities that allow attackers to access restricted files.

Implementation

PHP Code (upload.php):

<br><?php</p><p>if (isset($_POST['submit'])) {</p><pre class="brush:php;toolbar:false">// File type whitelist
$allowed_types = ['image/jpeg', 'image/jpg', 'image/png', 'image/gif'];

// Sanitize input
$file_name = $_FILES['image']['name'];
$file_type = $_FILES['image']['type'];
$file_size = $_FILES['image']['size'];

// Validate file type
if (!in_array($file_type, $allowed_types)) {
    echo "Invalid file type. Please upload an image.";
    exit;
}

// Validate file size
if ($file_size > 1000000) {
    echo "File too large. Maximum size allowed is 1MB.";
    exit;
}

// Verify image using GD library
$image_info = getimagesize($_FILES['image']['tmp_name']);

if (!$image_info) {
    echo "Invalid image. Please upload a valid image.";
    exit;
}

// Generate random file name and extension
$new_file_name = str_replace(".", "", microtime()) . "." . pathinfo($file_name, PATHINFO_EXTENSION);

// Isolated upload path outside document root
$upload_directory = 'uploads/';

// Save image to secure directory
if (!move_uploaded_file($_FILES['image']['tmp_name'], $upload_directory . $new_file_name)) {
    echo "Image upload failed. Please try again.";
    exit;
}

echo "Image uploaded successfully.";</p>
<p>}<br>?></p>
<p><form action="upload.php" method="post" enctype="multipart/form-data"></p>
<pre class="brush:php;toolbar:false"><input type="file" name="image">

<code>
<?php

// Sanitize input
$id = (int)($_GET['id'] ?? 0);

// Connect to database
$host = 'localhost';
$user = 'username';
$pass = 'password';
$db = 'database';

$db = new mysqli($host, $user, $pass, $db);

if ($db->connect_error) {
    echo "Database connection error: " . $db->connect_error;
    exit;
}

// Retrieve image details from database
$sql = "SELECT * FROM uploads WHERE id = ?";
$stmt = $db->prepare($sql);
$stmt->bind_param('i', $id);
$stmt->execute();

$result = $stmt->get_result()->fetch_assoc();

if (!$result) {
    echo "Invalid image ID.";
    exit;
}

header('Content-Type: ' . $result['mime_type']);
header('Content-Length: ' . filesize('uploads/' . $result['path']));
readfile('uploads/' . $result['path']);

$db->close();

Database Setup

Create a database with a table called "uploads" with the following columns:

• id (int) - Primary key
• path (text) - File path
• mime_type (text) - MIME type of the image

Post-Upload Actions

Once the image has been uploaded securely, there may be additional actions to consider, such as:

• Thumbnail Generation: Create smaller versions of the image for display in galleries, etc.
• Watermark: Add branding to prevent unauthorized distribution.
• Database Storage: Store image metadata and details for efficient retrieval.

Conclusion

By implementing the steps outlined in this article, you can significantly enhance the security of your image upload system and protect your website from potential vulnerabilities. The provided code and recommendations should serve as a solid foundation for your secure image upload implementation.

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