September 03, 2024

PHP Security & Best Practices (Security & Performance)

PHP has been a widely used language for developing web applications for decades now. Which is why it is important to adhere to best programming practices for PHP. Learn about recommended PHP practices for security and scalability.

PHP Best Practices & Security

PHP is one of the most popular programming languages widely used for creating dynamic websites. It empowers from small projects to large-scale CMS platforms like WordPress and frameworks like Laravel. The wide acceptance  and usage of PHP makes it important to write clean, reusable, secure and maintainable PHP code. In this post, we will discuss PHP best practices that every developer should follow to develop robust and scalable applications.

 

PHP Security & Best Practices for PHP Applications

Like in many other programming languages, PHP best practices are guidelines for writing clean, secure and maintainable code. These practices maximize PHP security, prevent vulnerabilities, improve performance and build scalable applications. Let's discuss some recommended practices that are essential as a standard for reducing PHP vulnerabilities in any web application.

 

1: Use The Latest PHP Version

With each new PHP version released come security fixes and new features, which is why it is one of the simplest ways to improve security by keeping the PHP version up-to-date and always staying ahead with critical security updates.

 

2: Follow PSR Coding Standards

The PHP Framework Interop Group (PHP-FIG) publishes PHP Standard Recommendations, abbreviated as PSRs. These recommendations define standards for PHP coding style and interfaces that should be followed. The following are the important PSRs to follow:

  1. PSR-1: Standard for basic coding style.
  2. PSR-4: Standard for autoloading.
  3. PSR-12: A guide for extended coding style.
 

3: Write Reusable and Modular Code

Think before developing an application, as it grows, there might be code that is used in several places. Break down the code into small granular functions and classes so it can be reused throughout the application. Following this strategy, you will have adapted the DRY (Don't Repeat Yourself) approach and have avoided code duplication.

 

4: Enforce HTTPS Across Web Application

One easy step to secure an application is to ensure the entire site runs over HTTPS and not just login pages. Use SSL/TLS certificates to encrypt data between client and server. The following steps can be taken for this:

  1. Redirect all HTTP requests to HTTPS.
  2. Use the Strict-Transport-Security header as an additional protection layer.
 

5: Sanitize and Validate User Input

Form submissions are one of the ways attackers may use to submit malicious data to a website. To reduce the risk of this vulnerability, always sanitize and validate user input to ensure data is in the expected format.

  1. Use filter_input(), filter_var() and filter_input_array() for filtering data.
  2. Validate URLs, emails, and phone numbers before processing and saving to the database.

An example of sanitizing and validating is as follows:

// Sanitize URL
header('Location: ' . filter_var($_SERVER['HTTP_REFERER'], FILTER_SANITIZE_URL));

// Validate email
$email = filter_input(INPUT_POST, 'email', FILTER_VALIDATE_EMAIL);
 

6: Prevent SQL Injection with Prepared Statements

One of the most common vulnerabilities is SQL injection, in which an attacker passes malformed data where user input is inserted into an SQL query. Which is why it is important to always use prepared SQL query statements, which separate the data from query logic and make it next to impossible for attackers to inject malicious SQL.

$stmt = $pdo->prepare("SELECT * FROM users WHERE email = :email");
$stmt->execute(['email' => $_POST['email']]);
 

7: Protect Against XSS Attacks

One of the other vulnerabilities in a web application is Cross-Site-Scripting (XSS), in which an attacker injects malicious script code into content that is delivered to the user. This happens for example, when a web page displays some data from a query parameter or it is already stored in the database. It is important to protect against XSS attacks with the following steps:

  1. Escape user input before displaying it, whether it is coming from the database or a query parameter.
  2. Add Content-Security-Policy header as an additional security layer.
// Example from query parameter
echo htmlspecialchars($_GET['comment'], ENT_QUOTES, 'UTF-8');

// Example if malicious code is stored in a variable i.e. coming from the database
echo htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');
 

8: Manage Sessions Properly

One of the PHP vulnerabilities is session hijacking, in which an attacker takes over a valid user session by stealing or manipulating the session ID. This makes it important to secure the PHP session and manage sessions properly. Steps to reduce the risk of session hijacking are:

  1. Use session_start() at the beginning of scripts.
  2. Use secure and HTTP only cookies.
  3. Regenerate the session ID after login.
// Secure session cookies
session_set_cookie_params([
    'secure' => true,        // Only sent over HTTPS
    'httponly' => true,      // Not accessible via JavaScript
    'samesite' => 'Strict',  // Prevent cross-site requests
]);

// Regenerate session ID
session_regenerate_id(true);
 

9: Store Hashed Passwords

One practice that every application follows already is storing hashed passwords. Even if the database gets compromised, the hashed passwords will be much harder to reverse than plain text. Always use password_hash() and password_verify() for user passwords.

$hash = password_hash($password, PASSWORD_DEFAULT);

if (password_verify($password, $hash)) {
    // Success
}
 

10: Use Recommended Security Headers

In addition to the mentioned practice, it is advisable to use HTTP security headers to prevent common attacks. The following headers in place can prevent common attacks:

header("Content-Security-Policy: default-src 'self';");
header("X-Frame-Options: DENY");
header("X-Content-Type-Options: nosniff");
header("Referrer-Policy: no-referrer");

We explained some of the recommended and best practices to secure a PHP application. By implementing these PHP security practices, the risk of common vulnerabilities can be reduced significantly.

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