XSS filtering function in PHP

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轮回少年
轮回少年 2020-11-27 11:18

Does anyone know of a good function out there for filtering generic input from forms? Zend_Filter_input seems to require prior knowledge of the contents of the input and I\'

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  • 2020-11-27 11:45

    I found a solution for my problem with the posts with german umlaut. To provide from totally cleaning (killing) the posts, i encode the incoming data:

        *$data = utf8_encode($data);
        ... function ...*
    

    And at last i decode the output to get correct signs:

        *$data = utf8_decode($data);*
    

    Now the post go through the filter function and i get a correct result...

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  • 2020-11-27 11:47

    Simple way? Use strip_tags():

    $str = strip_tags($input);
    

    You can also use filter_var() for that:

    $str = filter_var($input, FILTER_SANITIZE_STRING);
    

    The advantage of filter_var() is that you can control the behaviour by, for example, stripping or encoding low and high characters.

    Here is a list of sanitizing filters.

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  • 2020-11-27 11:50
    function clean($data){
        $data = rawurldecode($data);
        return filter_var($data, FILTER_SANITIZE_SPEC_CHARS);
    }
    
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  • 2020-11-27 11:56

    There are a number of ways hackers put to use for XSS attacks, PHP's built-in functions do not respond to all sorts of XSS attacks. Hence, functions such as strip_tags, filter_var, mysql_real_escape_string, htmlentities, htmlspecialchars, etc do not protect us 100%. You need a better mechanism, here is what is solution:

    function xss_clean($data)
    {
    // Fix &entity\n;
    $data = str_replace(array('&','<','>'), array('&','<','>'), $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;
    }
    
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