em Sem categoria

Função PHP para filtrar XSS ( cross site script )

A função abaixo foi desenvolvida por Kallahar’s e tem como objetivo filtrar tentativas de XSS.

Os créditos vão para : http://kallahar.com/smallprojects/php_xss_filter_function.php

 

function RemoveXSS($val) { 
   // 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> 
   $search = 'abcdefghijklmnopqrstuvwxyz'
   $search .= 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
   $search .= '[email protected]#$%^&*()'
   $search .= '~`";:?+/={}[]-_|\'\\'
   for ($i = 0; $i < strlen($search); $i++) { 
      // ;? matches the ;, which is optional 
      // 0{0,7} matches any padded zeros, which are optional and go up to 8 chars 
    
      // &#x0040 @ search for the hex values 
      $val = preg_replace('/(&#[xX]0{0,8}'.dechex(ord($search[$i])).';?)/i', $search[$i], $val); // with a ; 
      // &#00064 @ 0{0,7} matches '0' zero to seven times 
      $val = preg_replace('/(&#0{0,8}'.ord($search[$i]).';?)/', $search[$i], $val); // with a ; 
   } 
    
   // 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'); 
   $ra2 = Array('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'); 
   $ra = array_merge($ra1, $ra2); 
    
   $found = true; // keep replacing as long as the previous round replaced something 
   while ($found == true) { 
      $val_before = $val; 
      for ($i = 0; $i < sizeof($ra); $i++) { 
         $pattern = '/'
         for ($j = 0; $j < strlen($ra[$i]); $j++) { 
            if ($j > 0) { 
               $pattern .= '('
               $pattern .= '(&#[xX]0{0,8}([9ab]);)'
               $pattern .= '|'
               $pattern .= '|(&#0{0,8}([9|10|13]);)'
               $pattern .= ')*'
            } 
            $pattern .= $ra[$i][$j]; 
         } 
         $pattern .= '/i'
         $replacement = substr($ra[$i], 0, 2).'<x>'.substr($ra[$i], 2); // add in <> to nerf the tag 
         $val = preg_replace($pattern, $replacement, $val); // filter out the hex tags 
         if ($val_before == $val) { 
            // no replacements were made, so exit the loop 
            $found = false; 
         } 
      } 
   } 
   return $val; 
}