PHP Security Best Practices PT1

Coding (PHP 8)

Protecting Your Applications from Common Vulnerabilities

One of the first lesson I learned as a programmer is that it takes just a few second to screw up an application completely.

If someone decide to attack your code and you’re defence are not in place, there is little you can do about it.

I have heard of these stories many times in my career and I feel sorry everytime new ones add to the list.

Everybody focus on creating new application but I hear very few talking about defending it.

And it is surprising to see that considering how easy it is to get started.

So get ready to step into the shoes of a PHP superhero, 

The mission to protect web applications. 


In this blog post, we will explore PHP security best practices that will help you fortify your applications against common vulnerabilities.

Let’s dive in!


Input Validation and Sanitization 

One of the fundamental steps in securing your PHP applications is validating and sanitizing user input. 


By implementing robust input validation, you can prevent a wide range of attacks, including code injection and cross-site scripting (XSS). 

Begin by defining strict validation rules for each input field, checking for expected data types, length limits, and any specific patterns or formats. 


Another very useful thing that you can do is to utilize PHP’s filter functions and regular expressions to validate and sanitize user input effectively. 

Here’s an example of input sanitization using PHP 8’s built-in functions:


// Retrieve user input from a form field
$input = $_POST['email'];

// Sanitize the input using PHP 8's built-in functions
$sanitizedInput = filter_var($input, FILTER_SANITIZE_EMAIL);

// Check if the sanitized input is valid
if (filter_var($sanitizedInput, FILTER_VALIDATE_EMAIL)) {
    // The input is a valid email address after sanitization
    // Proceed with further processing or storage
    // ...
} else {
    // The input is not a valid email address after sanitization
    // Handle the invalid input accordingly
    // ...


In the example above, I assume that the user input is retrieved from a form field named email using the $_POST superglobal variable. 


The input is then sanitized using the filter_var() function with the FILTER_SANITIZE_EMAIL filter. 

This filter removes any potentially dangerous or unwanted characters from the input, ensuring that it conforms to the format of an email address.


After sanitization, we validate the sanitized input using the FILTER_VALIDATE_EMAIL filter to check if it is a valid email address. 

If the input passes the validation, it can be considered safe and used for further processing or storage. 

Otherwise, if the input fails the validation, you can handle the invalid input accordingly (e.g., display an error message to the user, log the incident, etc.).

You can read about filter_var in the official documentation.


By applying input sanitization using PHP 8’s built-in functions, you can help prevent code injection and mitigate the risks associated with malicious user input.


Remember, never trust user input and always validate and sanitize it before using it in your application


Protecting Against SQL Injection 

SQL injection is a prevalent attack vector where malicious actors manipulate SQL queries to gain unauthorized access to databases. 

To prevent SQL injection, adopt parameterized queries or prepared statements. 

These techniques allow you to separate SQL code from user input, making it impossible for attackers to inject malicious SQL statements. 


By binding user-supplied values as parameters, you ensure that they are treated as data rather than executable code. 

I have wrote about SQL injection on my blog already but I think it is better to see a concrete example of it.

Consider the following PHP code snippet that fetches user data from a MySQL database based on the user-supplied `username` parameter:


// Get the username from user input
$username = $_GET['username'];
// Construct the SQL query
$query = "SELECT * FROM users WHERE username = '$username'";
// Execute the query and fetch the user data
$result = mysqli_query($connection, $query);
$userData = mysqli_fetch_assoc($result);
// Display the user data
echo "Username: " . $userData['username'] . "
echo "Email: " . $userData['email'] . "


In the code above, the `username` parameter is directly concatenated into the SQL query string without any sanitization or validation. This leaves the application vulnerable to SQL injection attacks.


Now, consider an attacker who enters the following value for the `username` parameter: `’ OR ‘1’=’1' — `.

The resulting SQL query becomes:


SELECT * FROM users WHERE username = '' OR '1'='1' - '


In this case, the attacker’s input breaks out of the intended query structure by closing the single quotes, appending an OR condition that always evaluates to true (`’1'=’1'`), and commenting out the rest of the original query with  — .


As a result, the query fetches all rows from the `users` table instead of a specific user, potentially exposing sensitive information of all users.

To prevent SQL injection, you should use prepared statements or parameterized queries. 

Here’s an updated version of the code using prepared statements:


// Get the username from user input
$username = $_GET['username'];
// Prepare the SQL statement
$query = "SELECT * FROM users WHERE username = ?";
$stmt = mysqli_prepare($connection, $query);
mysqli_stmt_bind_param($stmt, "s", $username);
// Execute the statement and fetch the user data
$result = mysqli_stmt_get_result($stmt);
$userData = mysqli_fetch_assoc($result);
// Display the user data
echo "Username: " . $userData['username'] . "
echo "Email: " . $userData['email'] . "


By using prepared statements, the user input is treated as a parameter rather than being directly concatenated into the query. 

This prevents the SQL injection vulnerability, as the database engine understands that the user-supplied value is data, not part of the query structure.


Additionally, consider using PHP frameworks such as Symfony or Laravel as they include ORM (Object-Relational Mapping) libraries like Doctrine, which provide built-in protection against SQL injection.


Photo by sebastiaan stam on Unsplash


Cross-Site Scripting (XSS) Prevention 

Cross-Site Scripting (XSS) attacks occur when malicious scripts are injected into web pages viewed by users, compromising their session data or spreading malware. 

To reduce XSS vulnerabilities, implement output encoding and escaping techniques. 


Before displaying user-generated content, use PHP’s htmlspecialchars or htmlentities functions to encode special characters and prevent them from being interpreted as HTML or JavaScript. 


Implement Content Security Policy (CSP) to define trusted sources for scripts, stylesheets, and other resources, reducing the risk of XSS attacks

Here’s an example of a code snippet that demonstrates a Cross-Site Scripting (XSS) vulnerability:


// Get the user's name from a form field
$name = $_POST['name'];
// Display a welcome message with the user's name
echo "Welcome, " . $name . "!";


In the code above, the user’s name is retrieved from a form field using $_POST superglobal variable and then directly echoed back to the user without any sanitization or validation. 


This leaves the application vulnerable to XSS attacks.

Consider an attacker who enters the following name value: ``.

When the welcome message is displayed, the attacker’s input will be treated as HTML and executed as a script. 

This results in a pop-up alert showing the text “XSS Attack!”.

To prevent XSS attacks, you should apply output encoding or escaping techniques to ensure that user-generated content is treated as plain text rather than interpreted as HTML or JavaScript.


Here’s an updated version of the code using the htmlspecialchars() function to encode the user’s name before displaying it:


// Get the user's name from a form field
$name = $_POST['name'];
// Display a welcome message with the user's name (encoded)
echo "Welcome, " . htmlspecialchars($name, ENT_QUOTES, 'UTF-8') . "!";


By using htmlspecialchars(), special characters in the user’s name, such as `<`, `>`, and `&`, will be converted to their respective HTML entities, preventing them from being interpreted as HTML or JavaScript. 


This ensures that the user’s input is displayed as plain text and mitigates the risk of XSS attacks.

Remember to apply output encoding or escaping whenever you display user-generated content to protect against potential XSS vulnerabilities.


Securing User Authentication 

User authentication is a crucial aspect of web application security. 

When implementing user authentication in PHP, consider the following best practices. 


Firstly, store user passwords securely by using strong hashing algorithms like bcrypt or Argon2. 

bcrypt and Argon2 are both password hashing algorithms that are commonly used for securely storing and validating passwords. 


These algorithms are designed to be slow and computationally expensive, making it more difficult for attackers to guess or crack passwords through brute-force or dictionary-based attacks.

bcrypt is a widely used password hashing algorithm that has been around for many years. 

It incorporates the Blowfish encryption cipher in a modified form, making it suitable for password hashing. 


It is known for its adaptive nature, which means it can be configured to consume more computational resources as hardware improves. 


This property makes it resistant to brute-force attacks and keeps up with advancements in computing power. 

bcrypt also automatically handles the generation and management of salt, which enhances the security of hashed passwords.

On the other hand another password hashing algorithms is Argon2


Argon2 is a newer and more advanced password hashing algorithm that won the Password Hashing Competition in 2015. 

It is designed to be memory-hard, making it computationally expensive to compute hashes. 

It is resistant to both GPU-based and ASIC-based attacks, providing a higher level of security against evolving hardware capabilities. 

It also supports parallelism, allowing it to efficiently utilize multiple CPU cores during the hashing process. 

Has different variants: Argon2i for password hashing, Argon2d for password-based keys, and Argon2id which combines the benefits of both.


Both bcrypt and Argon2 are considered secure and recommended for password hashing. 


When using these algorithms, it is essential to employ a well-tested implementation in your programming language or framework of choice and ensure that you appropriately configure the algorithm’s parameters (such as cost factor or memory size) to strike a balance between security and performance.


Avoid outdated methods like MD5 or SHA1, which are no longer considered secure. 


Additionally, include salt values to further enhance password security. Enforce strong password policies and consider implementing two-factor authentication (2FA) for an additional layer of protection. 

Leverage PHP libraries like password_compat or dedicated authentication frameworks like Laravel’s built-in authentication system for streamlined implementation.



Securing your PHP applications requires a proactive and comprehensive approach. 

By implementing input validation and sanitization, protecting against SQL injection, preventing XSS attacks, and securing user authentication, you can significantly enhance the security posture of your applications. 


Remember to stay updated with the latest security practices, patch vulnerabilities promptly, and conduct regular security audits. 

By prioritizing security in your development process, you can safeguard your applications and ensure the protection of user data. 

Happy coding and stay secure!


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