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  1. <?php
  2. function RemoveXSS($val) {
  3.    // remove all non-printable characters. CR(0a) and LF(0b) and TAB(9) are allowed
  4.    // this prevents some character re-spacing such as <java\0script>
  5.    // note that you have to handle splits with \n, \r, and \t later since they *are* allowed in some inputs
  6.    $val = preg_replace('/([\x00-\x08,\x0b-\x0c,\x0e-\x19])/', '', $val);
  7.  
  8.    // straight replacements, the user should never need these since they're normal characters
  9.    // 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>
  10.    $search = 'abcdefghijklmnopqrstuvwxyz';
  11.    $search .= 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
  12.    $search .= '1234567890!@#$%^&*()';
  13.    $search .= '~`";:?+/={}[]-_|\'\\';
  14.    for ($i = 0; $i < strlen($search); $i++) {
  15.       // ;? matches the ;, which is optional
  16.       // 0{0,7} matches any padded zeros, which are optional and go up to 8 chars
  17.  
  18.       // &#x0040 @ search for the hex values
  19.       $val = preg_replace('/(&#[xX]0{0,8}'.dechex(ord($search[$i])).';?)/i', $search[$i], $val); // with a ;
  20.       // &#00064 @ 0{0,7} matches '0' zero to seven times
  21.       $val = preg_replace('/(&#0{0,8}'.ord($search[$i]).';?)/', $search[$i], $val); // with a ;
  22.    }
  23.  
  24.    // now the only remaining whitespace attacks are \t, \n, and \r
  25.    $ra1 = Array('javascript', 'vbscript', 'expression', 'applet', 'meta', 'xml', 'blink', 'link', 'style', 'script', 'embed', 'object', 'iframe', 'frame', 'frameset', 'ilayer', 'layer', 'bgsound', 'title', 'base');
  26.    $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');
  27.    $ra = array_merge($ra1, $ra2);
  28.  
  29.    $found = true; // keep replacing as long as the previous round replaced something
  30.    while ($found == true) {
  31.       $val_before = $val;
  32.       for ($i = 0; $i < sizeof($ra); $i++) {
  33.          $pattern = '/';
  34.          for ($j = 0; $j < strlen($ra[$i]); $j++) {
  35.             if ($j > 0) {
  36.                $pattern .= '(';
  37.                $pattern .= '(&#[xX]0{0,8}([9ab]);)';
  38.                $pattern .= '|';
  39.                $pattern .= '|(&#0{0,8}([9|10|13]);)';
  40.                $pattern .= ')*';
  41.             }
  42.             $pattern .= $ra[$i][$j];
  43.          }
  44.          $pattern .= '/i';
  45.          $replacement = substr($ra[$i], 0, 2).'<x>'.substr($ra[$i], 2); // add in <> to nerf the tag
  46.          $val = preg_replace($pattern, $replacement, $val); // filter out the hex tags
  47.          if ($val_before == $val) {
  48.             // no replacements were made, so exit the loop
  49.             $found = false;
  50.          }
  51.       }
  52.    }
  53.    return $val;
  54. } echo RemoveXSS("a <b onabort &#X61 > helo"); ?>
  55.  
  56.  
  57.  
  58.  
  59.  
Success #stdin #stdout 0.04s 13112KB
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Standard input is empty
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a <b on<x>abort a > helo
https://ideone.com/ax25u
language:
PHP (php 7.3.5)
created:
14 years ago
visibility:
public

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