What are some common pitfalls in PHP code, as demonstrated in the provided script?

One common pitfall in PHP code is the use of insecure input validation, which can lead to vulnerabilities such as SQL injection attacks. To solve this issue, it is important to always sanitize and validate user input before using it in database queries or other sensitive operations. 

// Example of insecure input validation
$username = $_POST['username'];
$password = $_POST['password'];

$query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = mysqli_query($connection, $query);

// Fixed code with secure input validation
$username = mysqli_real_escape_string($connection, $_POST['username']);
$password = mysqli_real_escape_string($connection, $_POST['password']);

$query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = mysqli_query($connection, $query);

Keywords

syntax error undefined variable SQL injection XSS vulnerability infinite loop

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