Database input sanitisation with PHP forms

Question

I sanitise the data I receive from the form in the following way:

$gender = filter_var($_POST['gender'], FILTER_SANITIZE_STRING);
$firstName = filter_var($_POST['firstName'], FILTER_SANITIZE_STRING);
$lastName = filter_var($_POST['lastName'], FILTER_SANITIZE_STRING);
$email = filter_var($_POST['email'], FILTER_SANITIZE_EMAIL);
$message = filter_var($_POST['comment'], FILTER_SANITIZE_STRING);
$address = filter_var($_POST['address'], FILTER_SANITIZE_STRING);
$numBrochures = (int) filter_var($_POST['quantity'], FILTER_SANITIZE_NUMBER_INT);

The relevant SQL queries that insert the data are as follows:

if (mysqli_query($conn, "INSERT INTO users(firstName, lastName, email, gender) VALUES('$firstName', '$lastName', '$email', '$gender')") == TRUE) {
  logSuccess($file, "Adding user");
}
else {
  logError($file, "Adding user", mysqli_error($conn));
}

$userId = $conn->query("SELECT `userId` FROM users WHERE `firstName` = '$firstName' AND `lastName` = '$lastName' AND `email` = '$email'")->fetch_object()->userId;
if ($userId == false) {
  logError($file, "Fetching user id", mysqli_error($conn));

}

if (mysqli_query($conn, "INSERT INTO brochureOrders(userId, address, numBrochures, message) VALUES('$userId', '$address', '$numBrochures', '$message')") == TRUE) {
  logSuccess($file, "Brochure Order");
  $sendConfirmationEmail = true;
}
else {
  logError($file, "Brochure Order", mysqli_error($conn));
}

However, in my database, I see entries like the following:

address = "vz8y8E  gghwptvvzuak, [url=http://ytvsmximkjnp.com/]ytvsmximkjnp[/url], [link=http://hiabgyvsjifp.com/]hiabgyvsjifp[/link], http://tyvylndqitoy.com/"

Shouldn't the following have taken care of this?

$address = filter_var($_POST['address'], FILTER_SANITIZE_STRING);

Could someone tell me what I am doing incorrectly here?

filter_var with the 'FILTER_SANITIZE_STRING' filter just strips tags and (optionally) strips or encodes special characters. What were you hoping that it would do? — George Cummins
– George Cummins, Commented Dec 9, 2014 at 18:33
It doesn't do that. As Arian suggests, you should begin using prepared statements via PDO immediately to protect against SQL injection attacks, and write or find a better filtering scheme to remove URLs as needed. — George Cummins
– George Cummins, Commented Dec 9, 2014 at 18:35

Arian Faurtosh · Accepted Answer · 2014-12-09 18:44:44Z

1

Because the OP stated in the comments he wants to switch to prepared statement, I thought I'd show him an example.

Instead of something like this:

if (mysqli_query($conn, "INSERT INTO users(firstName, lastName, email, gender) VALUES('$firstName', '$lastName', '$email', '$gender')") == TRUE) {
  logSuccess($file, "Adding user");
}
else {
  logError($file, "Adding user", mysqli_error($conn));
}

Do something like this:

$query = "INSERT INTO users (firstName, lastName, email, gender) VALUES(?, ?, ?, ?)";

if($stmt = $mysqli->prepare($query)){
    $stmt->bind_param('ssss', $firstName, $lastName, $email, $gender);
    $stmt->exeucte();
    $stmt->close();
}else die("Failed to prepare!");

and this

$query = "SELECT `userId` FROM users WHERE `firstName` = ? AND `lastName` = ? AND `email` = ?";

if($stmt = $mysqli->prepare($query)){
    $stmt->bind_param('sss', $firstName, $lastName, $email);
    $stmt->execute();
    $stmt->bind_result($userId);
    $stmt->fetch();
    $stmt->close()
}else die("Failed to prepare!");

edited Dec 9, 2014 at 18:44

answered Dec 9, 2014 at 18:36

Arian Faurtosh

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2 Comments

George Cummins Over a year ago

This is a good improvement to prevent SQL injection attacks, but be aware that it doesn't address the core issue as stated in comments: "I was hoping for it to remove URLs."

Arian Faurtosh Over a year ago

@GeorgeCummins yeah i know, but the OP stated in the comments he wanted to switch to prepared statements, so I just wanted to show him an example of what it would look like.

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