I'm using these functions to filter all my input variables. I was quite confident it would protect my website from possible XSS and SQL injections, but there are still vulnerabilities.
Please suggest improvements for my filter code.
//filter input field
function cleanMe($data) {
// normalize $data because of get_magic_quotes_gpc
$dataNeedsStripSlashes = get_magic_quotes_gpc();
if ($dataNeedsStripSlashes) {
$data = stripslashes($data);
}
// normalize $data because of whitespace on beginning and end
$data = trim($data);
// strip tags
$data = strip_tags($data);
// replace characters with their HTML entitites
$data = htmlentities($data);
// mysql escape string
$data = mysql_real_escape_string($data);
//call xss clean
$data=xss_clean($data);
return $data;
}
function xss_clean($data)
{
// Fix &entity\n;
$data = str_replace(array('&','<','>'), array('&amp;','&lt;','&gt;'), $data);
$data = preg_replace('/(&#*\w+)[\x00-\x20]+;/u', '$1;', $data);
$data = preg_replace('/(&#x*[0-9A-F]+);*/iu', '$1;', $data);
$data = html_entity_decode($data, ENT_COMPAT, 'UTF-8');
// Remove any attribute starting with "on" or xmlns
$data = preg_replace('#(<[^>]+?[\x00-\x20"\'])(?:on|xmlns)[^>]*+>#iu', '$1>', $data);
// Remove javascript: and vbscript: protocols
$data = preg_replace('#([a-z]*)[\x00-\x20]*=[\x00-\x20]*([`\'"]*)[\x00-\x20]*j[\x00-\x20]*a[\x00-\x20]*v[\x00-\x20]*a[\x00-\x20]*s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:#iu', '$1=$2nojavascript...', $data);
$data = preg_replace('#([a-z]*)[\x00-\x20]*=([\'"]*)[\x00-\x20]*v[\x00-\x20]*b[\x00-\x20]*s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:#iu', '$1=$2novbscript...', $data);
$data = preg_replace('#([a-z]*)[\x00-\x20]*=([\'"]*)[\x00-\x20]*-moz-binding[\x00-\x20]*:#u', '$1=$2nomozbinding...', $data);
// Only works in IE: <span style="width: expression(alert('Ping!'));"></span>
$data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?expression[\x00-\x20]*\([^>]*+>#i', '$1>', $data);
$data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?behaviour[\x00-\x20]*\([^>]*+>#i', '$1>', $data);
$data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:*[^>]*+>#iu', '$1>', $data);
// Remove namespaced elements (we do not need them)
$data = preg_replace('#</*\w+:\w[^>]*+>#i', '', $data);
do
{
// Remove really unwanted tags
$old_data = $data;
$data = preg_replace('#</*(?:applet|b(?:ase|gsound|link)|embed|frame(?:set)?|i(?:frame|layer)|l(?:ayer|ink)|meta|object|s(?:cript|tyle)|title|xml)[^>]*+>#i', '', $data);
}
while ($old_data !== $data);
// we are done...
return $data;
}
htmlentities
and/orstrip_tags
is totally sufficient... not sure what's going on in your code but it looks really messy. – frankster Aug 31 '14 at 15:53mysql_real_escape
is only safe when set the encoding likemysql_set_charset('UTF-8');
RegEx doesn't seem safe either. – DanFromGermany Aug 31 '14 at 15:53html_entity_decode
which is basically the inverse ofhtmlentities
. – Gumbo Aug 31 '14 at 15:58