What best practices should be followed to prevent backdoor vulnerabilities in PHP code?

Backdoor vulnerabilities in PHP code can be prevented by following best practices such as validating user input, using parameterized queries for database interactions to prevent SQL injection, avoiding the use of eval() function, and keeping software and libraries up to date with regular security patches. 

// Example of preventing backdoor vulnerabilities by validating user input
$user_input = $_POST['user_input'];

// Validate user input before using it
if (filter_var($user_input, FILTER_VALIDATE_INT)) {
    // Proceed with using the validated user input
} else {
    // Handle invalid input
}

Keywords

SQL injection cross-site scripting input validation secure coding authentication.

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