PHP CodeBase: 过滤XSS攻击的PHP函数

那么PHP站点如何防御XSS攻击呢？

下面的函数可以用来过滤用户的输入，保证输入是XSS安全的。具体如何过滤，可以参看函数内部，也有注释。

<?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 <javascript>  
   // note that you have to handle splits with , , and 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=@avascript:alert("XSS")>  
   $search = "abcdefghijklmnopqrstuvwxyz";
   $search .= "ABCDEFGHIJKLMNOPQRSTUVWXYZ";  
   $search .= "1234567890!@#$%^&*()";
   $search .= "~`";:?+/={}[]-_|"\";
   for ($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
    
      // @ @ search for the hex values
      $val = preg_replace("/(&#[xX]0{0,8}".dechex(ord($search[$i])).";?)/i", $search[$i], $val); // with a ;
      // @ @ 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 , , and
   $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;  
}   
?>

PHP CodeBase 代码库计划，一般一次收集一个函数，解决一个问题。