bcit-ci/CodeIgniter

##############
Security Class
##############

The Security Class contains methods that help you create a secure
application, processing input data for security.

.. contents::
  :local:

.. raw:: html

  <div class="custom-index container"></div>

*************
XSS Filtering
*************

CodeIgniter comes with a Cross Site Scripting prevention filter, which
looks for commonly used techniques to trigger JavaScript or other types
of code that attempt to hijack cookies or do other malicious things.
If anything disallowed is encountered it is rendered safe by converting
the data to character entities.

To filter data through the XSS filter use the ``xss_clean()`` method::

    $data = $this->security->xss_clean($data);

An optional second parameter, *is_image*, allows this function to be used
to test images for potential XSS attacks, useful for file upload
security. When this second parameter is set to TRUE, instead of
returning an altered string, the function returns TRUE if the image is
safe, and FALSE if it contained potentially malicious information that a
browser may attempt to execute.

::

    if ($this->security->xss_clean($file, TRUE) === FALSE)
    {
        // file failed the XSS test
    }

.. important:: If you want to filter HTML attribute values, use
    :php:func:`html_escape()` instead!

*********************************
Cross-site request forgery (CSRF)
*********************************

You can enable CSRF protection by altering your **application/config/config.php**
file in the following way::

    $config['csrf_protection'] = TRUE;

If you use the :doc:`form helper <../helpers/form_helper>`, then
:func:`form_open()` will automatically insert a hidden csrf field in
your forms. If not, then you can use ``get_csrf_token_name()``
and ``get_csrf_hash()``
::

    $csrf = array(
        'name' => $this->security->get_csrf_token_name(),
        'hash' => $this->security->get_csrf_hash()
    );

    ...

    <input type="hidden" name="<?=$csrf['name'];?>" value="<?=$csrf['hash'];?>" />

Tokens may be either regenerated on every submission (default) or
kept the same throughout the life of the CSRF cookie. The default
regeneration of tokens provides stricter security, but may result
in usability concerns as other tokens become invalid (back/forward
navigation, multiple tabs/windows, asynchronous actions, etc). You
may alter this behavior by editing the following config parameter

::

    $config['csrf_regenerate'] = TRUE;

Select URIs can be whitelisted from csrf protection (for example API
endpoints expecting externally POSTed content). You can add these URIs
by editing the 'csrf_exclude_uris' config parameter::

    $config['csrf_exclude_uris'] = array('api/person/add');

Regular expressions are also supported (case-insensitive)::

    $config['csrf_exclude_uris'] = array(
        'api/record/[0-9]+',
        'api/title/[a-z]+'
    );

***************
Class Reference
***************

.. php:class:: CI_Security

    .. php:method:: xss_clean($str[, $is_image = FALSE])

        :param    mixed    $str: Input string or an array of strings
        :returns:    XSS-clean data
        :rtype:    mixed

        Tries to remove XSS exploits from the input data and returns the cleaned string.
        If the optional second parameter is set to true, it will return boolean TRUE if
        the image is safe to use and FALSE if malicious data was detected in it.

        .. important:: This method is not suitable for filtering HTML attribute values!
            Use :php:func:`html_escape()` for that instead.

    .. php:method:: sanitize_filename($str[, $relative_path = FALSE])

        :param    string    $str: File name/path
        :param    bool    $relative_path: Whether to preserve any directories in the file path
        :returns:    Sanitized file name/path
        :rtype:    string

        Tries to sanitize filenames in order to prevent directory traversal attempts
        and other security threats, which is particularly useful for files that were supplied via user input.
        ::

            $filename = $this->security->sanitize_filename($this->input->post('filename'));

        If it is acceptable for the user input to include relative paths, e.g.
        *file/in/some/approved/folder.txt*, you can set the second optional parameter, ``$relative_path`` to TRUE.
        ::

            $filename = $this->security->sanitize_filename($this->input->post('filename'), TRUE);

    .. php:method:: get_csrf_token_name()

        :returns:    CSRF token name
        :rtype:    string

        Returns the CSRF token name (the ``$config['csrf_token_name']`` value).

    .. php:method:: get_csrf_hash()

        :returns:    CSRF hash
        :rtype:    string

        Returns the CSRF hash value. Useful in combination with ``get_csrf_token_name()``
        for manually building forms or sending valid AJAX POST requests.

    .. php:method:: entity_decode($str[, $charset = NULL])

        :param    string    $str: Input string
        :param    string    $charset: Character set of the input string
        :returns:    Entity-decoded string
        :rtype:    string

        This method acts a lot like PHP's own native ``html_entity_decode()`` function in ENT_COMPAT mode, only
        it tries to detect HTML entities that don't end in a semicolon because some browsers allow that.

        If the ``$charset`` parameter is left empty, then your configured ``$config['charset']`` value will be used.

    .. php:method:: get_random_bytes($length)

        :param    int    $length: Output length
        :returns:    A binary stream of random bytes or FALSE on failure
        :rtype:    string

        A convenience method for getting proper random bytes via ``mcrypt_create_iv()``,
        ``/dev/urandom`` or ``openssl_random_pseudo_bytes()`` (in that order), if one
        of them is available.

        Used for generating CSRF and XSS tokens.

        .. note:: The output is NOT guaranteed to be cryptographically secure,
            just the best attempt at that.