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what is a good method to sanitize the whole $_POST array in php?

Posted by: admin April 23, 2020 Leave a comment

Questions:

I have a form with a lot of variables which is then sending an email, rather than sanitizing each $_POST value with filter_var($_POST['var'], FILTER_SANITIZE_STRING); I was after a more simple piece of code. I came up with the below, which seems to work as I believe the default action is FILTER_SANITIZE_STRING, but I was just wondering what peoples opinions are, and if this is not good practice, perhaps you could tell me why? The $_POST values are then individually embedded into new variables, so I would only be using array_map just at the start to sanitize everything…

$_POST = array_map('filter_var', $_POST);

Thank you for your replies, to give you a little more information, basically:

I have 20-30 input fields in a form which are being captured,
the data is then displayed to the user to check their input,
variables are then sanitized,
the user is then sent an email
and then finally the details are entered into a db.

currently I am sanitizing using the above array_map function, as well as FILTER_SANITIZE_EMAIL on the email address before sending an email and then escaping the input using mysql_real_escape_string() before the insert into the db. Without getting into prepared statements etc.. do you think I should be doing anything additionally? thanks again!

How to&Answers:

If the type of each of your input variables is a string and you want to sanitize them all at once, you can use:

// prevent XSS
$_GET   = filter_input_array(INPUT_GET, FILTER_SANITIZE_STRING);
$_POST  = filter_input_array(INPUT_POST, FILTER_SANITIZE_STRING);

This will sanitize your $_GET and $_POST arrays.

Seen here: PHP -Sanitize values of a array

Answer:

Depends what its being used for.

If you are inserting it into the database then mysql_real_escape_string() for quoted strings and type casting for numbers would be the way to go – well ideally prepared statements, but thats an entirely different matter.

If you plan on outputting the data onto the webpage then I would recommend something like htmlspecialchars()

If you plan on using the user input as a shell argument, then you would use escapeshellarg()

Moving onto your question about sending emails. Well, the following should suffice:

filter_var($_POST['message'], FILTER_SANITIZE_STRING);

All this does is basically strip tags and encode special characters.

Answer:

There is no correct way to do blanket sanitation. What sanitation method you need depends on what is done to the data.

Sanitize the data directly before it is used.

Answer:

This is what I use in all my projects:

function util_array_trim(array &$array, $filter = false)
{
    array_walk_recursive($array, function (&$value) use ($filter) {
        $value = trim($value);
        if ($filter) {
            $value = filter_var($value, FILTER_SANITIZE_STRING);
        }
    });

    return $array;
}

It allows to trim and sanitize a nested array of posted data

Answer:

To apply specific filters on multiple fields, use a switch statement.

$post  = filter_input_array(INPUT_POST, FILTER_SANITIZE_STRING);

foreach($post as $k => $v) {
    switch ($k) {
        case 'int_1':
        case 'int_2':
            $post[$k] = filter_var($v, FILTER_SANITIZE_NUMBER_INT) * 1;
            break;
        case 'float_1':
        case 'float_2':
            $post[$k] = filter_var($v, FILTER_SANITIZE_NUMBER_FLOAT, FILTER_FLAG_ALLOW_FRACTION) * 1;
            break;
        default:
            break;
    }
}

Note: My IDE (NetBeans) warns about using global $_POST anywhere as a security violation, so I’ve just gotten into the habit of using a local $post variable instead. If you choose not to do the blanket string sanitation first, FILTER_SANITIZE_STRING could be used for the default: case.