What aspects should be considered to ensure application security?

To ensure the security of a PHP application, the following aspects should be considered:

• Validation and filtering of data: always check and sanitize input data to prevent SQL injections, XSS, and other attacks.
• Use of prepared statements when working with databases to prevent SQL injections.
• Session protection: use secure cookies, regenerate session identifiers, and limit session lifetime.
• Error handling: do not display detailed error messages to users to avoid revealing the internal structure of the application.
• Encryption and password storage: use modern hashing algorithms, such as password_hash() and password_verify().
• Access control and authentication: implement strict permission checks.
• Updates and patches: timely update PHP and used libraries to fix known vulnerabilities.

Example of using prepared statements:

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

Following these practices will significantly enhance your application's security.