What are some common pitfalls when working with PHP code like the one provided in the forum thread?

Issue: The provided PHP code is vulnerable to SQL injection attacks due to directly inserting user input into the SQL query. To prevent this, you should use prepared statements with parameterized queries. 

// 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);

Keywords

syntax error undefined variable SQL injection XSS vulnerability infinite loop

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