What potential security risks are present in the PHP code provided for the login functionality?

The potential security risks present in the PHP code for the login functionality include vulnerability to SQL injection attacks due to the use of unsanitized user input in the SQL query. To solve this issue, we should use prepared statements with parameterized queries to prevent SQL injection attacks.

// Original vulnerable code
$username = $_POST['username'];
$password = $_POST['password'];

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

// Fixed code using prepared statements
$username = $_POST['username'];
$password = $_POST['password'];

$query = "SELECT * FROM users WHERE username=? AND password=?";
$stmt = mysqli_prepare($connection, $query);
mysqli_stmt_bind_param($stmt, "ss", $username, $password);
mysqli_stmt_execute($stmt);
$result = mysqli_stmt_get_result($stmt);