What are the best practices for writing secure code in PHP?

1 Use HTTPS

One of the simplest and most effective ways to secure your PHP code is to use HTTPS instead of HTTP for your web pages. HTTPS encrypts the data that is sent and received between your server and your clients, making it harder for hackers to intercept, modify, or steal it. HTTPS also helps you avoid the risk of mixed content, which occurs when your web page loads some resources over HTTP and some over HTTPS, creating a security loophole. To use HTTPS, you need to obtain and install a valid SSL certificate for your domain and configure your server to redirect all HTTP requests to HTTPS.

2 Validate and sanitize input

Another common source of security issues in PHP is user input. User input can come from various sources, such as forms, query strings, cookies, or headers, and it can contain malicious code or data that can compromise your server or database. To prevent this, you need to validate and sanitize all user input before using it in your code. Validation means checking if the input meets certain criteria, such as format, length, or type, and rejecting it if it does not. Sanitization means removing or escaping any unwanted or dangerous characters or tags from the input, such as quotes, slashes, or HTML. You can use built-in PHP functions, such as filter_var, filter_input, or htmlspecialchars, to perform validation and sanitization.

3 Use prepared statements

One of the most common and dangerous attacks on PHP applications is SQL injection, which occurs when a hacker inserts SQL commands into user input that is then executed by your database. SQL injection can allow hackers to access, modify, or delete your data, or even take over your server. To prevent SQL injection, you need to use prepared statements instead of concatenating user input into your SQL queries. Prepared statements separate the query structure from the user input, making it impossible for hackers to inject SQL commands. You can use PHP extensions, such as PDO or mysqli, to create and execute prepared statements.

4 Use secure passwords

Another best practice for writing secure code in PHP is to use secure passwords for your database, your server, and your user accounts. Secure passwords are long, complex, and unique, and they should not be based on personal information or common words. You should also avoid storing passwords in plain text or using weak hashing algorithms, such as MD5 or SHA1, to encrypt them. Instead, you should use strong hashing algorithms, such as bcrypt or argon2, that are designed for password security and that use salt and iterations to make them harder to crack. You can use PHP functions, such as password_hash and password_verify, to create and check hashed passwords.

5 Use proper error handling

Another source of security vulnerabilities in PHP is improper error handling. Error handling refers to how your code responds to unexpected or exceptional situations, such as missing files, invalid input, or database failures. Improper error handling can expose sensitive information, such as file paths, database credentials, or code logic, to hackers or users, or cause your application to crash or behave unpredictably. To avoid this, you need to use proper error handling techniques, such as try-catch blocks, custom error handlers, or error logging, to catch and handle errors gracefully and discreetly. You should also disable error reporting and display in your production environment and use PHP constants, such as E_ALL or E_ERROR, to control the level of error reporting in your development environment.

6 Use updated software

The last best practice for writing secure code in PHP is to use updated software for your server, your database, and your PHP version. Updated software contains the latest security patches and fixes that can protect your code from known vulnerabilities and exploits. You should also use secure and reliable software that follows the industry standards and best practices for web security, such as TLS, CSP, or HSTS. You can use tools, such as Composer or NPM, to manage your dependencies and libraries and keep them updated as well.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?