新增安全过滤类

application/common.php

@@ -408,3 +408,13 @@ if (!function_exists('check_cors_request')) {
         }
     }
 }
+
+if (!function_exists('xss_clean')) {
+    /**
+     * 清理XSS
+     */
+    function xss_clean($content, $is_image = false)
+    {
+        return \app\common\library\Security::instance()->xss_clean($content, $is_image);
+    }
+}

application/common/library/Security.php

@@ -0,0 +1,874 @@
+<?php
+
+namespace app\common\library;
+
+use Exception;
+
+/**
+ * 安全过滤类
+ *
+ * @category       Security
+ * @copyright      Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)
+ * @copyright      Copyright (c) 2014 - 2019, British Columbia Institute of Technology (https://bcit.ca/)
+ * @license        https://opensource.org/licenses/MIT MIT License
+ * @link           https://codeigniter.com
+ * @author         EllisLab Dev Team
+ */
+class Security
+{
+
+    protected static $instance = null;
+
+    /**
+     * List of sanitize filename strings
+     *
+     * @var    array
+     */
+    public $filename_bad_chars = array(
+        '../',
+        '<!--',
+        '-->',
+        '<',
+        '>',
+        "'",
+        '"',
+        '&',
+        '$',
+        '#',
+        '{',
+        '}',
+        '[',
+        ']',
+        '=',
+        ';',
+        '?',
+        '%20',
+        '%22',
+        '%3c',        // <
+        '%253c',    // <
+        '%3e',        // >
+        '%0e',        // >
+        '%28',        // (
+        '%29',        // )
+        '%2528',    // (
+        '%26',        // &
+        '%24',        // $
+        '%3f',        // ?
+        '%3b',        // ;
+        '%3d'        // =
+    );
+
+    /**
+     * Character set
+     *
+     * Will be overridden by the constructor.
+     *
+     * @var    string
+     */
+    public $charset = 'UTF-8';
+
+    /**
+     * XSS Hash
+     *
+     * Random Hash for protecting URLs.
+     *
+     * @var    string
+     */
+    protected $_xss_hash;
+
+    /**
+     * List of never allowed strings
+     *
+     * @var    array
+     */
+    protected $_never_allowed_str = array(
+        'document.cookie'   => '[removed]',
+        '(document).cookie' => '[removed]',
+        'document.write'    => '[removed]',
+        '(document).write'  => '[removed]',
+        '.parentNode'       => '[removed]',
+        '.innerHTML'        => '[removed]',
+        '-moz-binding'      => '[removed]',
+        '<!--'              => '&lt;!--',
+        '-->'               => '--&gt;',
+        '<![CDATA['         => '&lt;![CDATA[',
+        '<comment>'         => '&lt;comment&gt;',
+        '<%'                => '&lt;&#37;'
+    );
+
+    /**
+     * List of never allowed regex replacements
+     *
+     * @var    array
+     */
+    protected $_never_allowed_regex = array(
+        'javascript\s*:',
+        '(\(?document\)?|\(?window\)?(\.document)?)\.(location|on\w*)',
+        'expression\s*(\(|&\#40;)', // CSS and IE
+        'vbscript\s*:', // IE, surprise!
+        'wscript\s*:', // IE
+        'jscript\s*:', // IE
+        'vbs\s*:', // IE
+        'Redirect\s+30\d',
+        "([\"'])?data\s*:[^\\1]*?base64[^\\1]*?,[^\\1]*?\\1?"
+    );
+
+    protected $options = [
+        'placeholder' => '[removed]'
+    ];
+
+    /**
+     * Class constructor
+     *
+     * @return    void
+     */
+    public function __construct($options = [])
+    {
+        $this->options = array_merge($this->options, $options);
+        foreach ($this->_never_allowed_str as $index => &$item) {
+            $item = str_replace('[removed]', $this->options['placeholder'], $item);
+        }
+    }
+
+    /**
+     *
+     * @param array $options 参数
+     * @return Security
+     */
+    public static function instance($options = [])
+    {
+        if (is_null(self::$instance)) {
+            self::$instance = new static($options);
+        }
+
+        return self::$instance;
+    }
+
+    /**
+     * XSS Clean
+     *
+     * Sanitizes data so that Cross Site Scripting Hacks can be
+     * prevented.  This method does a fair amount of work but
+     * it is extremely thorough, designed to prevent even the
+     * most obscure XSS attempts.  Nothing is ever 100% foolproof,
+     * of course, but I haven't been able to get anything passed
+     * the filter.
+     *
+     * Note: Should only be used to deal with data upon submission.
+     *     It's not something that should be used for general
+     *     runtime processing.
+     *
+     * @link    http://channel.bitflux.ch/wiki/XSS_Prevention
+     *        Based in part on some code and ideas from Bitflux.
+     *
+     * @link    http://ha.ckers.org/xss.html
+     *        To help develop this script I used this great list of
+     *        vulnerabilities along with a few other hacks I've
+     *        harvested from examining vulnerabilities in other programs.
+     *
+     * @param string|string[] $str      Input data
+     * @param bool            $is_image Whether the input is an image
+     * @return    string
+     */
+    public function xss_clean($str, $is_image = false)
+    {
+        // Is the string an array?
+        if (is_array($str)) {
+            foreach ($str as $key => &$value) {
+                $str[$key] = $this->xss_clean($value);
+            }
+
+            return $str;
+        }
+
+        // Remove Invisible Characters
+        $str = $this->remove_invisible_characters($str);
+
+        /*
+         * URL Decode
+         *
+         * Just in case stuff like this is submitted:
+         *
+         * <a href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a>
+         *
+         * Note: Use rawurldecode() so it does not remove plus signs
+         */
+        if (stripos($str, '%') !== false) {
+            do {
+                $oldstr = $str;
+                $str = rawurldecode($str);
+                $str = preg_replace_callback('#%(?:\s*[0-9a-f]){2,}#i', array($this, '_urldecodespaces'), $str);
+            } while ($oldstr !== $str);
+            unset($oldstr);
+        }
+
+        /*
+         * Convert character entities to ASCII
+         *
+         * This permits our tests below to work reliably.
+         * We only convert entities that are within tags since
+         * these are the ones that will pose security problems.
+         */
+        $str = preg_replace_callback("/[^a-z0-9>]+[a-z0-9]+=([\'\"]).*?\\1/si", array($this, '_convert_attribute'), $str);
+        $str = preg_replace_callback('/<\w+.*/si', array($this, '_decode_entity'), $str);
+
+        // Remove Invisible Characters Again!
+        $str = $this->remove_invisible_characters($str);
+
+        /*
+         * Convert all tabs to spaces
+         *
+         * This prevents strings like this: ja	vascript
+         * NOTE: we deal with spaces between characters later.
+         * NOTE: preg_replace was found to be amazingly slow here on
+         * large blocks of data, so we use str_replace.
+         */
+        $str = str_replace("\t", ' ', $str);
+
+        // Capture converted string for later comparison
+        $converted_string = $str;
+
+        // Remove Strings that are never allowed
+        $str = $this->_do_never_allowed($str);
+
+        /*
+         * Makes PHP tags safe
+         *
+         * Note: XML tags are inadvertently replaced too:
+         *
+         * <?xml
+         *
+         * But it doesn't seem to pose a problem.
+         */
+        if ($is_image === true) {
+            // Images have a tendency to have the PHP short opening and
+            // closing tags every so often so we skip those and only
+            // do the long opening tags.
+            $str = preg_replace('/<\?(php)/i', '&lt;?\\1', $str);
+        } else {
+            $str = str_replace(array('<?', '?' . '>'), array('&lt;?', '?&gt;'), $str);
+        }
+
+        /*
+         * Compact any exploded words
+         *
+         * This corrects words like:  j a v a s c r i p t
+         * These words are compacted back to their correct state.
+         */
+        $words = array(
+            'javascript',
+            'expression',
+            'vbscript',
+            'jscript',
+            'wscript',
+            'vbs',
+            'script',
+            'base64',
+            'applet',
+            'alert',
+            'document',
+            'write',
+            'cookie',
+            'window',
+            'confirm',
+            'prompt',
+            'eval'
+        );
+
+        foreach ($words as $word) {
+            $word = implode('\s*', str_split($word)) . '\s*';
+
+            // We only want to do this when it is followed by a non-word character
+            // That way valid stuff like "dealer to" does not become "dealerto"
+            $str = preg_replace_callback('#(' . substr($word, 0, -3) . ')(\W)#is', array($this, '_compact_exploded_words'), $str);
+        }
+
+        /*
+         * Remove disallowed Javascript in links or img tags
+         * We used to do some version comparisons and use of stripos(),
+         * but it is dog slow compared to these simplified non-capturing
+         * preg_match(), especially if the pattern exists in the string
+         *
+         * Note: It was reported that not only space characters, but all in
+         * the following pattern can be parsed as separators between a tag name
+         * and its attributes: [\d\s"\'`;,\/\=\(\x00\x0B\x09\x0C]
+         * ... however, $this->remove_invisible_characters() above already strips the
+         * hex-encoded ones, so we'll skip them below.
+         */
+        do {
+            $original = $str;
+
+            if (preg_match('/<a/i', $str)) {
+                $str = preg_replace_callback('#<a(?:rea)?[^a-z0-9>]+([^>]*?)(?:>|$)#si', array($this, '_js_link_removal'), $str);
+            }
+
+            if (preg_match('/<img/i', $str)) {
+                $str = preg_replace_callback('#<img[^a-z0-9]+([^>]*?)(?:\s?/?>|$)#si', array($this, '_js_img_removal'), $str);
+            }
+
+            if (preg_match('/script|xss/i', $str)) {
+                $str = preg_replace('#</*(?:script|xss).*?>#si', $this->options['placeholder'], $str);
+            }
+        } while ($original !== $str);
+        unset($original);
+
+        /*
+         * Sanitize naughty HTML elements
+         *
+         * If a tag containing any of the words in the list
+         * below is found, the tag gets converted to entities.
+         *
+         * So this: <blink>
+         * Becomes: &lt;blink&gt;
+         */
+        $pattern = '#'
+            . '<((?<slash>/*\s*)((?<tagName>[a-z0-9]+)(?=[^a-z0-9]|$)|.+)' // tag start and name, followed by a non-tag character
+            . '[^\s\042\047a-z0-9>/=]*' // a valid attribute character immediately after the tag would count as a separator
+            // optional attributes
+            . '(?<attributes>(?:[\s\042\047/=]*' // non-attribute characters, excluding > (tag close) for obvious reasons
+            . '[^\s\042\047>/=]+' // attribute characters
+            // optional attribute-value
+            . '(?:\s*=' // attribute-value separator
+            . '(?:[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*))' // single, double or non-quoted value
+            . ')?' // end optional attribute-value group
+            . ')*)' // end optional attributes group
+            . '[^>]*)(?<closeTag>\>)?#isS';
+
+        // Note: It would be nice to optimize this for speed, BUT
+        //       only matching the naughty elements here results in
+        //       false positives and in turn - vulnerabilities!
+        do {
+            $old_str = $str;
+            $str = preg_replace_callback($pattern, array($this, '_sanitize_naughty_html'), $str);
+        } while ($old_str !== $str);
+        unset($old_str);
+
+        /*
+         * Sanitize naughty scripting elements
+         *
+         * Similar to above, only instead of looking for
+         * tags it looks for PHP and JavaScript commands
+         * that are disallowed. Rather than removing the
+         * code, it simply converts the parenthesis to entities
+         * rendering the code un-executable.
+         *
+         * For example:	eval('some code')
+         * Becomes:	eval&#40;'some code'&#41;
+         */
+        $str = preg_replace(
+            '#(alert|prompt|confirm|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si',
+            '\\1\\2&#40;\\3&#41;',
+            $str
+        );
+
+        // Same thing, but for "tag functions" (e.g. eval`some code`)
+        $str = preg_replace(
+            '#(alert|prompt|confirm|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)`(.*?)`#si',
+            '\\1\\2&#96;\\3&#96;',
+            $str
+        );
+
+        // Final clean up
+        // This adds a bit of extra precaution in case
+        // something got through the above filters
+        $str = $this->_do_never_allowed($str);
+
+        /*
+         * Images are Handled in a Special Way
+         * - Essentially, we want to know that after all of the character
+         * conversion is done whether any unwanted, likely XSS, code was found.
+         * If not, we return TRUE, as the image is clean.
+         * However, if the string post-conversion does not matched the
+         * string post-removal of XSS, then it fails, as there was unwanted XSS
+         * code found and removed/changed during processing.
+         */
+        if ($is_image === true) {
+            return ($str === $converted_string);
+        }
+
+        return $str;
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * XSS Hash
+     *
+     * Generates the XSS hash if needed and returns it.
+     *
+     * @return    string    XSS hash
+     */
+    public function xss_hash()
+    {
+        if ($this->_xss_hash === null) {
+            $rand = $this->get_random_bytes(16);
+            $this->_xss_hash = ($rand === false)
+                ? md5(uniqid(mt_rand(), true))
+                : bin2hex($rand);
+        }
+
+        return $this->_xss_hash;
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * Get random bytes
+     *
+     * @param int $length Output length
+     * @return    string
+     */
+    public function get_random_bytes($length)
+    {
+        if (empty($length) OR !ctype_digit((string)$length)) {
+            return false;
+        }
+
+        if (function_exists('random_bytes')) {
+            try {
+                // The cast is required to avoid TypeError
+                return random_bytes((int)$length);
+            } catch (Exception $e) {
+                // If random_bytes() can't do the job, we can't either ...
+                // There's no point in using fallbacks.
+                return false;
+            }
+        }
+
+        // Unfortunately, none of the following PRNGs is guaranteed to exist ...
+        if (defined('MCRYPT_DEV_URANDOM') && ($output = mcrypt_create_iv($length, MCRYPT_DEV_URANDOM)) !== false) {
+            return $output;
+        }
+
+
+        if (is_readable('/dev/urandom') && ($fp = fopen('/dev/urandom', 'rb')) !== false) {
+            // Try not to waste entropy ...
+            stream_set_chunk_size($fp, $length);
+            $output = fread($fp, $length);
+            fclose($fp);
+            if ($output !== false) {
+                return $output;
+            }
+        }
+
+        if (function_exists('openssl_random_pseudo_bytes')) {
+            return openssl_random_pseudo_bytes($length);
+        }
+
+        return false;
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * HTML Entities Decode
+     *
+     * A replacement for html_entity_decode()
+     *
+     * The reason we are not using html_entity_decode() by itself is because
+     * while it is not technically correct to leave out the semicolon
+     * at the end of an entity most browsers will still interpret the entity
+     * correctly. html_entity_decode() does not convert entities without
+     * semicolons, so we are left with our own little solution here. Bummer.
+     *
+     * @link    https://secure.php.net/html-entity-decode
+     *
+     * @param string $str     Input
+     * @param string $charset Character set
+     * @return    string
+     */
+    public function entity_decode($str, $charset = null)
+    {
+        if (strpos($str, '&') === false) {
+            return $str;
+        }
+
+        static $_entities;
+
+        isset($charset) OR $charset = $this->charset;
+        isset($_entities) OR $_entities = array_map('strtolower', get_html_translation_table(HTML_ENTITIES, ENT_COMPAT | ENT_HTML5, $charset));
+
+        do {
+            $str_compare = $str;
+
+            // Decode standard entities, avoiding false positives
+            if (preg_match_all('/&[a-z]{2,}(?![a-z;])/i', $str, $matches)) {
+                $replace = array();
+                $matches = array_unique(array_map('strtolower', $matches[0]));
+                foreach ($matches as &$match) {
+                    if (($char = array_search($match . ';', $_entities, true)) !== false) {
+                        $replace[$match] = $char;
+                    }
+                }
+
+                $str = str_replace(array_keys($replace), array_values($replace), $str);
+            }
+
+            // Decode numeric & UTF16 two byte entities
+            $str = html_entity_decode(
+                preg_replace('/(&#(?:x0*[0-9a-f]{2,5}(?![0-9a-f;])|(?:0*\d{2,4}(?![0-9;]))))/iS', '$1;', $str),
+                ENT_COMPAT | ENT_HTML5,
+                $charset
+            );
+        } while ($str_compare !== $str);
+        return $str;
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * Sanitize Filename
+     *
+     * @param string $str           Input file name
+     * @param bool   $relative_path Whether to preserve paths
+     * @return    string
+     */
+    public function sanitize_filename($str, $relative_path = false)
+    {
+        $bad = $this->filename_bad_chars;
+
+        if (!$relative_path) {
+            $bad[] = './';
+            $bad[] = '/';
+        }
+
+        $str = $this->remove_invisible_characters($str, false);
+
+        do {
+            $old = $str;
+            $str = str_replace($bad, '', $str);
+        } while ($old !== $str);
+
+        return stripslashes($str);
+    }
+
+    // ----------------------------------------------------------------
+
+    /**
+     * Strip Image Tags
+     *
+     * @param string $str
+     * @return    string
+     */
+    public function strip_image_tags($str)
+    {
+        return preg_replace(
+            array(
+                '#<img[\s/]+.*?src\s*=\s*(["\'])([^\\1]+?)\\1.*?\>#i',
+                '#<img[\s/]+.*?src\s*=\s*?(([^\s"\'=<>`]+)).*?\>#i'
+            ),
+            '\\2',
+            $str
+        );
+    }
+
+    // ----------------------------------------------------------------
+
+    /**
+     * URL-decode taking spaces into account
+     *
+     * @param array $matches
+     * @return    string
+     */
+    protected function _urldecodespaces($matches)
+    {
+        $input = $matches[0];
+        $nospaces = preg_replace('#\s+#', '', $input);
+        return ($nospaces === $input)
+            ? $input
+            : rawurldecode($nospaces);
+    }
+
+    // ----------------------------------------------------------------
+
+    /**
+     * Compact Exploded Words
+     *
+     * Callback method for xss_clean() to remove whitespace from
+     * things like 'j a v a s c r i p t'.
+     *
+     * @param array $matches
+     * @return    string
+     */
+    protected function _compact_exploded_words($matches)
+    {
+        return preg_replace('/\s+/s', '', $matches[1]) . $matches[2];
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * Sanitize Naughty HTML
+     *
+     * Callback method for xss_clean() to remove naughty HTML elements.
+     *
+     * @param array $matches
+     * @return    string
+     */
+    protected function _sanitize_naughty_html($matches)
+    {
+        static $naughty_tags = array(
+            'alert',
+            'area',
+            'prompt',
+            'confirm',
+            'applet',
+            'audio',
+            'basefont',
+            'base',
+            'behavior',
+            'bgsound',
+            'blink',
+            'body',
+            'embed',
+            'expression',
+            'form',
+            'frameset',
+            'frame',
+            'head',
+            'html',
+            'ilayer',
+            'iframe',
+            'input',
+            'button',
+            'select',
+            'isindex',
+            'layer',
+            'link',
+            'meta',
+            'keygen',
+            'object',
+            'plaintext',
+            'style',
+            'script',
+            'textarea',
+            'title',
+            'math',
+            'video',
+            'svg',
+            'xml',
+            'xss'
+        );
+
+        static $evil_attributes = array(
+            'on\w+',
+            'style',
+            'xmlns',
+            'formaction',
+            'form',
+            'xlink:href',
+            'FSCommand',
+            'seekSegmentTime'
+        );
+
+        // First, escape unclosed tags
+        if (empty($matches['closeTag'])) {
+            return '&lt;' . $matches[1];
+        } // Is the element that we caught naughty? If so, escape it
+        elseif (in_array(strtolower($matches['tagName']), $naughty_tags, true)) {
+            return '&lt;' . $matches[1] . '&gt;';
+        } // For other tags, see if their attributes are "evil" and strip those
+        elseif (isset($matches['attributes'])) {
+            // We'll store the already filtered attributes here
+            $attributes = array();
+
+            // Attribute-catching pattern
+            $attributes_pattern = '#'
+                . '(?<name>[^\s\042\047>/=]+)' // attribute characters
+                // optional attribute-value
+                . '(?:\s*=(?<value>[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*)))' // attribute-value separator
+                . '#i';
+
+            // Blacklist pattern for evil attribute names
+            $is_evil_pattern = '#^(' . implode('|', $evil_attributes) . ')$#i';
+
+            // Each iteration filters a single attribute
+            do {
+                // Strip any non-alpha characters that may precede an attribute.
+                // Browsers often parse these incorrectly and that has been a
+                // of numerous XSS issues we've had.
+                $matches['attributes'] = preg_replace('#^[^a-z]+#i', '', $matches['attributes']);
+
+                if (!preg_match($attributes_pattern, $matches['attributes'], $attribute, PREG_OFFSET_CAPTURE)) {
+                    // No (valid) attribute found? Discard everything else inside the tag
+                    break;
+                }
+
+                if (
+                    // Is it indeed an "evil" attribute?
+                    preg_match($is_evil_pattern, $attribute['name'][0])
+                    // Or does it have an equals sign, but no value and not quoted? Strip that too!
+                    OR (trim($attribute['value'][0]) === '')
+                ) {
+                    $attributes[] = 'xss=removed';
+                } else {
+                    $attributes[] = $attribute[0][0];
+                }
+
+                $matches['attributes'] = substr($matches['attributes'], $attribute[0][1] + strlen($attribute[0][0]));
+            } while ($matches['attributes'] !== '');
+
+            $attributes = empty($attributes)
+                ? ''
+                : ' ' . implode(' ', $attributes);
+            return '<' . $matches['slash'] . $matches['tagName'] . $attributes . '>';
+        }
+
+        return $matches[0];
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * JS Link Removal
+     *
+     * Callback method for xss_clean() to sanitize links.
+     *
+     * This limits the PCRE backtracks, making it more performance friendly
+     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
+     * PHP 5.2+ on link-heavy strings.
+     *
+     * @param array $match
+     * @return    string
+     */
+    protected function _js_link_removal($match)
+    {
+        return str_replace(
+            $match[1],
+            preg_replace(
+                '#href=.*?(?:(?:alert|prompt|confirm)(?:\(|&\#40;|`|&\#96;)|javascript:|livescript:|mocha:|charset=|window\.|\(?document\)?\.|\.cookie|<script|<xss|d\s*a\s*t\s*a\s*:)#si',
+                '',
+                $this->_filter_attributes($match[1])
+            ),
+            $match[0]
+        );
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * JS Image Removal
+     *
+     * Callback method for xss_clean() to sanitize image tags.
+     *
+     * This limits the PCRE backtracks, making it more performance friendly
+     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
+     * PHP 5.2+ on image tag heavy strings.
+     *
+     * @param array $match
+     * @return    string
+     */
+    protected function _js_img_removal($match)
+    {
+        return str_replace(
+            $match[1],
+            preg_replace(
+                '#src=.*?(?:(?:alert|prompt|confirm|eval)(?:\(|&\#40;|`|&\#96;)|javascript:|livescript:|mocha:|charset=|window\.|\(?document\)?\.|\.cookie|<script|<xss|base64\s*,)#si',
+                '',
+                $this->_filter_attributes($match[1])
+            ),
+            $match[0]
+        );
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * Attribute Conversion
+     *
+     * @param array $match
+     * @return    string
+     */
+    protected function _convert_attribute($match)
+    {
+        return str_replace(array('>', '<', '\\'), array('&gt;', '&lt;', '\\\\'), $match[0]);
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * Filter Attributes
+     *
+     * Filters tag attributes for consistency and safety.
+     *
+     * @param string $str
+     * @return    string
+     */
+    protected function _filter_attributes($str)
+    {
+        $out = '';
+        if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches)) {
+            foreach ($matches[0] as $match) {
+                $out .= preg_replace('#/\*.*?\*/#s', '', $match);
+            }
+        }
+
+        return $out;
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * HTML Entity Decode Callback
+     *
+     * @param array $match
+     * @return    string
+     */
+    protected function _decode_entity($match)
+    {
+        // Protect GET variables in URLs
+        // 901119URL5918AMP18930PROTECT8198
+        $match = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-/]+)|i', $this->xss_hash() . '\\1=\\2', $match[0]);
+
+        // Decode, then un-protect URL GET vars
+        return str_replace(
+            $this->xss_hash(),
+            '&',
+            $this->entity_decode($match, $this->charset)
+        );
+    }
+
+    // --------------------------------------------------------------------
+
+    /**
+     * Do Never Allowed
+     *
+     * @param string
+     * @return    string
+     */
+    protected function _do_never_allowed($str)
+    {
+        $str = str_replace(array_keys($this->_never_allowed_str), $this->_never_allowed_str, $str);
+
+        foreach ($this->_never_allowed_regex as $regex) {
+            $str = preg_replace('#' . $regex . '#is', $this->options['placeholder'], $str);
+        }
+
+        return $str;
+    }
+
+    /**
+     * Remove Invisible Characters
+     */
+    public function remove_invisible_characters($str, $url_encoded = true)
+    {
+        $non_displayables = array();
+
+        // every control character except newline (dec 10),
+        // carriage return (dec 13) and horizontal tab (dec 09)
+        if ($url_encoded) {
+            $non_displayables[] = '/%0[0-8bcef]/i';    // url encoded 00-08, 11, 12, 14, 15
+            $non_displayables[] = '/%1[0-9a-f]/i';    // url encoded 16-31
+            $non_displayables[] = '/%7f/i';    // url encoded 127
+        }
+
+        $non_displayables[] = '/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]+/S';    // 00-08, 11, 12, 14-31, 127
+
+        do {
+            $str = preg_replace($non_displayables, '', $str, -1, $count);
+        } while ($count);
+
+        return $str;
+    }
+
+}