RemoveXSS.php

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<?php
/**
 * Usage: Run *every* variable passed in through it.
 * The goal of this function is to be a generic function that can be used to
 * parse almost any input and render it XSS safe. For more information on
 * actual XSS attacks, check out http://ha.ckers.org/xss.html. Another
 * excellent site is the XSS Database which details each attack and how it
 * works.
 *
 * Used with permission by the author.
 * URL: http://quickwired.com/smallprojects/php_xss_filter_function.php
 *
 * Check XSS attacks on http://ha.ckers.org/xss.html
 *
 * License:
 * This code is public domain, you are free to do whatever you want with it,
 * including adding it to your own project which can be under any license.
 *
 * $Id: RemoveXSS.php 10547 2011-02-22 20:03:57Z lolli $
 *
 * @author  Travis Puderbaugh <kallahar@quickwired.com>
 * @author  Jigal van Hemert <jigal@xs4all.nl>
 * @package RemoveXSS
 */
final class RemoveXSS {

    /**
     * Removes potential XSS code from an input string.
     *
     * Using an external class by Travis Puderbaugh <kallahar@quickwired.com>
     *
     * @param   string      Input string
     * @param   string      replaceString for inserting in keywords (which destroyes the tags)
     * @return  string      Input string with potential XSS code removed
     */
    public static function process($val, $replaceString = '<x>') {
        // don't use empty $replaceString because then no XSS-remove will be done
        if ($replaceString == '') {
            $replaceString = '<x>';
        }
        // remove all non-printable characters. CR(0a) and LF(0b) and TAB(9) are allowed
        // this prevents some character re-spacing such as <java\0script>
        // note that you have to handle splits with \n, \r, and \t later since they *are* allowed in some inputs
        $val = preg_replace('/([\x00-\x08][\x0b-\x0c][\x0e-\x19])/', '', $val);

        // straight replacements, the user should never need these since they're normal characters
        // this prevents like <IMG SRC=&#X40&#X61&#X76&#X61&#X73&#X63&#X72&#X69&#X70&#X74&#X3A&#X61&#X6C&#X65&#X72&#X74&#X28&#X27&#X58&#X53&#X53&#X27&#X29>
        $searchHexEncodings = '/&#[xX]0{0,8}(21|22|23|24|25|26|27|28|29|2a|2b|2d|2f|30|31|32|33|34|35|36|37|38|39|3a|3b|3d|3f|40|41|42|43|44|45|46|47|48|49|4a|4b|4c|4d|4e|4f|50|51|52|53|54|55|56|57|58|59|5a|5b|5c|5d|5e|5f|60|61|62|63|64|65|66|67|68|69|6a|6b|6c|6d|6e|6f|70|71|72|73|74|75|76|77|78|79|7a|7b|7c|7d|7e);?/ie';
        $searchUnicodeEncodings = '/&#0{0,8}(33|34|35|36|37|38|39|40|41|42|43|45|47|48|49|50|51|52|53|54|55|56|57|58|59|61|63|64|65|66|67|68|69|70|71|72|73|74|75|76|77|78|79|80|81|82|83|84|85|86|87|88|89|90|91|92|93|94|95|96|97|98|99|100|101|102|103|104|105|106|107|108|109|110|111|112|113|114|115|116|117|118|119|120|121|122|123|124|125|126);?/ie';
        while (preg_match($searchHexEncodings, $val) || preg_match($searchUnicodeEncodings, $val)) {
            $val = preg_replace($searchHexEncodings, "chr(hexdec('\\1'))", $val);
            $val = preg_replace($searchUnicodeEncodings, "chr('\\1')", $val);
        }

        // now the only remaining whitespace attacks are \t, \n, and \r
        $ra1 = array('javascript', 'vbscript', 'expression', 'applet', 'meta', 'xml', 'blink', 'link', 'style', 'script', 'embed', 'object', 'iframe', 'frame', 'frameset', 'ilayer', 'layer', 'bgsound', 'title', 'base', 'onabort', 'onactivate', 'onafterprint', 'onafterupdate', 'onbeforeactivate', 'onbeforecopy', 'onbeforecut', 'onbeforedeactivate', 'onbeforeeditfocus', 'onbeforepaste', 'onbeforeprint', 'onbeforeunload', 'onbeforeupdate', 'onblur', 'onbounce', 'oncellchange', 'onchange', 'onclick', 'oncontextmenu', 'oncontrolselect', 'oncopy', 'oncut', 'ondataavailable', 'ondatasetchanged', 'ondatasetcomplete', 'ondblclick', 'ondeactivate', 'ondrag', 'ondragend', 'ondragenter', 'ondragleave', 'ondragover', 'ondragstart', 'ondrop', 'onerror', 'onerrorupdate', 'onfilterchange', 'onfinish', 'onfocus', 'onfocusin', 'onfocusout', 'onhelp', 'onkeydown', 'onkeypress', 'onkeyup', 'onlayoutcomplete', 'onload', 'onlosecapture', 'onmousedown', 'onmouseenter', 'onmouseleave', 'onmousemove', 'onmouseout', 'onmouseover', 'onmouseup', 'onmousewheel', 'onmove', 'onmoveend', 'onmovestart', 'onpaste', 'onpropertychange', 'onreadystatechange', 'onreset', 'onresize', 'onresizeend', 'onresizestart', 'onrowenter', 'onrowexit', 'onrowsdelete', 'onrowsinserted', 'onscroll', 'onselect', 'onselectionchange', 'onselectstart', 'onstart', 'onstop', 'onsubmit', 'onunload');
        $ra_tag = array('applet', 'meta', 'xml', 'blink', 'link', 'style', 'script', 'embed', 'object', 'iframe', 'frame', 'frameset', 'ilayer', 'layer', 'bgsound', 'title', 'base');
        $ra_attribute = array('style', 'onabort', 'onactivate', 'onafterprint', 'onafterupdate', 'onbeforeactivate', 'onbeforecopy', 'onbeforecut', 'onbeforedeactivate', 'onbeforeeditfocus', 'onbeforepaste', 'onbeforeprint', 'onbeforeunload', 'onbeforeupdate', 'onblur', 'onbounce', 'oncellchange', 'onchange', 'onclick', 'oncontextmenu', 'oncontrolselect', 'oncopy', 'oncut', 'ondataavailable', 'ondatasetchanged', 'ondatasetcomplete', 'ondblclick', 'ondeactivate', 'ondrag', 'ondragend', 'ondragenter', 'ondragleave', 'ondragover', 'ondragstart', 'ondrop', 'onerror', 'onerrorupdate', 'onfilterchange', 'onfinish', 'onfocus', 'onfocusin', 'onfocusout', 'onhelp', 'onkeydown', 'onkeypress', 'onkeyup', 'onlayoutcomplete', 'onload', 'onlosecapture', 'onmousedown', 'onmouseenter', 'onmouseleave', 'onmousemove', 'onmouseout', 'onmouseover', 'onmouseup', 'onmousewheel', 'onmove', 'onmoveend', 'onmovestart', 'onpaste', 'onpropertychange', 'onreadystatechange', 'onreset', 'onresize', 'onresizeend', 'onresizestart', 'onrowenter', 'onrowexit', 'onrowsdelete', 'onrowsinserted', 'onscroll', 'onselect', 'onselectionchange', 'onselectstart', 'onstart', 'onstop', 'onsubmit', 'onunload');
        $ra_protocol = array('javascript', 'vbscript', 'expression');

        //remove the potential &#xxx; stuff for testing
        $val2 = preg_replace('/(&#[xX]?0{0,8}(9|10|13|a|b);)*\s*/i', '', $val);
        $ra = array();

        foreach ($ra1 as $ra1word) {
            //stripos is faster than the regular expressions used later
            //and because the words we're looking for only have chars < 0x80
            //we can use the non-multibyte safe version
            if (stripos($val2, $ra1word ) !== false ) {
                //keep list of potential words that were found
                if (in_array($ra1word, $ra_protocol)) {
                    $ra[] = array($ra1word, 'ra_protocol');
                }
                if (in_array($ra1word, $ra_tag)) {
                    $ra[] = array($ra1word, 'ra_tag');
                }
                if (in_array($ra1word, $ra_attribute)) {
                    $ra[] = array($ra1word, 'ra_attribute');
                }
                //some keywords appear in more than one array
                //these get multiple entries in $ra, each with the appropriate type
            }
        }
        //only process potential words
        if (count($ra) > 0) {
            // keep replacing as long as the previous round replaced something
            $found = true;
            while ($found == true) {
                $val_before = $val;
                for ($i = 0; $i < sizeof($ra); $i++) {
                    $pattern = '';
                    for ($j = 0; $j < strlen($ra[$i][0]); $j++) {
                        if ($j > 0) {
                            $pattern .= '((&#[xX]0{0,8}([9ab]);)|(&#0{0,8}(9|10|13);)|\s)*';
                        }
                        $pattern .= $ra[$i][0][$j];
                    }
                    //handle each type a little different (extra conditions to prevent false positives a bit better)
                    switch ($ra[$i][1]) {
                        case 'ra_protocol':
                            //these take the form of e.g. 'javascript:'
                            $pattern .= '((&#[xX]0{0,8}([9ab]);)|(&#0{0,8}(9|10|13);)|\s)*(?=:)';
                            break;
                        case 'ra_tag':
                            //these take the form of e.g. '<SCRIPT[^\da-z] ....';
                            $pattern = '(?<=<)' . $pattern . '((&#[xX]0{0,8}([9ab]);)|(&#0{0,8}(9|10|13);)|\s)*(?=[^\da-z])';
                            break;
                        case 'ra_attribute':
                            //these take the form of e.g. 'onload='  Beware that a lot of characters are allowed
                            //between the attribute and the equal sign!
                            $pattern .= '[\s\!\#\$\%\&\(\)\*\~\+\-\_\.\,\:\;\?\@\[\/\|\\\\\]\^\`]*(?==)';
                            break;
                    }
                    $pattern = '/' . $pattern . '/i';
                    // add in <x> to nerf the tag
                    $replacement = substr_replace($ra[$i][0], $replaceString, 2, 0);
                    // filter out the hex tags
                    $val = preg_replace($pattern, $replacement, $val);
                    if ($val_before == $val) {
                        // no replacements were made, so exit the loop
                        $found = false;
                    }
                }
            }
        }

        return $val;
    }
}

?>