anvil_php/app/core/Security.php

<?php if(!defined('APP_ROOT')) exit('No direct script access allowed');

/** Security Class
 *  Pretty heavily based on the CodeIgniter Security Class
 */
class Security {
  /* Random Hash for protecting URLs */
  protected $_xss_hash = '';
  /* Random Hash for Cross-Site Request Forgery Protection Cookie (CSRFPC) */
  protected $_csrf_hash = '';
  /* Expiration time for CSRFPC */
  protected $_csrf_expire = 7200;
  /* Token name for CSRFPC */
  protected $_csrf_token_name = 'anvil_csrf_token';
  /* Cookie name for CSRFPC */
  protected $_csrf_cookie_name = 'anvil_csrf_token';
  /* List of never allowed strings */
  protected $_never_allowed_str = array(
      'document.cookie' => '[removed]',
      'document.write' => '[removed]',
      '.parentNode' => '[removed]',
      '.innerHTML' => '[removed]',
      'window.location' => '[removed]',
      '-moz-binding' => '[removed]',
      '<!--' => '&lt;!--',
      '-->' => '--&gt;',
      '<![CDATA[' => '&lt;![CDATA[',
      '<comment>' => '&lt;comment&gt;'
  );

  /* List of never allowed regex replacement */
  protected $_never_allowed_regex = array(
      'javascript\s*:',
      'expression\s*(\(|&\#40;)', // CSS and IE
      'vbscript\s*:', // IE, surprise!
      'Redirect\s+302',
      "([\"'])?data\s*:[^\\1]*?base64[^\\1]*?,[^\\1]*?,[^\\1]*?\\1?"
  );

  protected $_anvil;
  /* Constructor */
  public function __construct($a) {
    $this->_anvil = $a;
    // Is CSRF protection enabled?
    if($this->_anvil->config->item('csrf_protection')===TRUE) {
      // Set the CSRF hash
      $this->_csrf_set_hash();
    }
    // Security class initialized
  }

  /**
   * Verify CSRF Protection
   */
  public function csrf_verify() {
    // If it's not a POST request we will set the CSRF cookie
    if($this->_anvil->request->type !== 'POST') {
      return $this->csrf_set_cookie();
    }

    // Do the tokens exist in both the POST params and COOKIE array?
    if(isset($this->_anvil->request->parameters[$this->_csrf_token_name],
             $this->_anvil->cookie[$this->_csrf_cookie_name])) {
      $this->csrf_show_error();
    }

    // Do the tokens match?
    if($this->_anvil->request->parameters[$this->_csrf_token_name] !=
        $this->_anvil->request->cookie[$this->_csrf_cookie_name]) {
      $this->csrf_show_error();
    }

    // We kill this since we're done and we don't want to polute the POST array
    unset($this->_anvil->request->parameters[$this->_csrf_token_name]);

    // None of these things should last forever
    unset($this->_anvil->request->cookie[$this->_csrf_cookie_name]);
    $this->_csrf_set_hash();
    $this->csrf_set_cookie();

    return $this;
  }

  /** Set CSRF Protection Cookie */
  public function csrf_set_cookie() {
    $expire = time() + $this->_csrf_expire;
    $secure_cookie = ($this->_anvil->config->item('cookie_secure') === TRUE ? 1 : 0);
    if($secure_cookie && !$this->_anvil->request->isSecure()) {
      return FALSE;
    }

    $this->_anvil->request->setCookie($this->_csrf_cookie_name, $this->_csrf_hash, $expire, NULL, NULL, $secure_cookie);
    return $this;
  }

  /* Get CSRF Hash */
  public function get_csrf_hash() {
    return $this->_csrf_hash;
  }

  /* Get CSRF Token Name */
  public function get_csrf_token_name() {
    return $this->_csrf_token_name;
  }

  /**
   * XSS Clean
   * Sanitizes data so that CSS hacks can be prevented.
   * This function does a fair amount of work but it is
   * extremely thorough, designed to prevent even the
   * most obscure XSS attempts. Nothing is ever 100%
   * foolproof, of course, but I haven't been able to
   * get anything passed the filter.
   *
   * Note: This function should only be used to deal
   * with data upon submission. It's not something that
   * should be used for general runtime processing.
   *
   * @param   mixed string or array
   * @param   bool
   * @return  string
   */
  public function xss_clean($str, $is_image = FALSE) {
    /* Is the string an array? */
    if(is_array($str)) {
      while(list($key) = each($str)) {
        $str[$key] = $this->xss_clean($str[$key]);
      }
      return $str;
    }

    /* Remove Invisible Characters */
    $str = remove_invisible_characters($str);

    /* Validate Entities in URLs */
    $str = $this->_validate_entities($str);

    /* URL Decode
     * Note: Use rawurldecode() so it does not remove plus signs
     */
    $str = rawurldecode($str);

    /* Convert character entities to ASCII
     * This permits our tests below to work reliably
     * We only convert entities that are within tags since
     * these are the ones that will pose security problems
     */
    $str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", array($this, '_convert_attribute'), $str);
    $str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", array($this, '_decode_entity'), $str);

    /* Remove Invisible Characters AGAIN! */
    $str = remove_invisible_characters($str);

    /* Convert all tabs to spaces
     * This prevents strings like this: ja  vascript
     * NOTE: we deal with spaces between characters later.
     * NOTE: preg_replace was found to be amazingly slow here on
     * large blocks of data, so we use str_replace.
     */
    if(strpos($str, "\t") !== FALSE) {
      $str = str_replace("\t", ' ', $str);
    }

    /* Capture converted string for later comparison */
    $converted_string = $str;

    /* Remove Strings that are never allowed */
    $str = $this->_do_never_allowed($str);

    /* Makes PHP tags safe
     * Note: XML tags are inadvertently replaced too:
     * <?xml
     * But it doesn't seem to pose a problem.
     */
    if($is_image === TRUE) {
      /* Images have a tendency to have the PHP short opening and
       * closing tags every so often so we skip those and only
       * do the long opening tags.
       */
      $str = preg_replace('/<\?(php)/i', "&lt;?\\1", $str);
    } else {
      $str = str_replace(array('<?', '?'.'>'), array('&lt;?', '?&gt;'), $str);
    }

    /* Compact any exploded words
     * This corrects words like: j a v a s c r i p t
     * These words are compacted back to their correct state.
     */
    $words = array(
      'javascript', 'expression', 'vbscript', 'script', 'base64',
      'applet', 'alert', 'document', 'write', 'cookie', 'window'
    );

    foreach($words as $word) {
      $temp = '';
      for($i = 0, $wordlen = strlen($word); $i < $wordlen; $i++) {
        $temp .= substr($word, $i, 1)."\s*";
      }

      // We only want to do this when it is followed by a non-word character
      // That way valid stuff like "dealer to" does not become "dealerto"
      $str = preg_replace_callback('#('.substr($temp, 0, -3).')(\W)#is', array($this, '_compact_exploded_words'), $str);
    }

    /* Remove disallowed Javascript in links or img tags */
    do {
      $original = $str;
      if(preg_match("/<a/i", $str)) {
        $str = preg_replace_callback("#<a\s+([^>]*?)(>|$)#si", array($this, '_js_link_removal'), $str);
      }
      if(preg_match("/<img/i", $str)) {
        $str = preg_replace_callback("#<img\s+([^>]*?)(\s?/?\>|$)#si", array($this, '_js_img_removal'), $str);
      }
      if(preg_match("/script/i", $str) || preg_match("/xss/i", $str)) {
        $str = preg_replace("#<(/*)(script|xss)(.*?)\>#si", '[removed]', $str);
      }
    } while($original != $str);
    unset($original);

    // Remove evil attributes such as style, onclick and xmlns
    $str = $this->_remove_evil_attributes($str, $is_image);

    /* Sanitize naughty HTML elements
     * If a tag containing any of the words in the list
     * below is found, the tag gets converted to entities.
     * so this: <blink>
     * becoms: &lt;blink&gt;
     */
    $naughty = 'alert|applet|audio|basefont|base|behavior|bgsound|blink|body|embed|expression|form|frameset|frame|head|html|ilayer|iframe|input|isindex|layer|link|meta|object|plaintext|style|script|textarea|title|video|xml|xss';
    $str = preg_replace_callback('#<(/*\s*)('.$naughty.')([^><]*)([><]*)#is', array($this, '_sanitize_naughty_html'), $str);

    /* Sanitize naughty scripting elements
     * Similar to above, only instead of looking for
     * tags it looks for PHP and JavaScript commands
     * that are disallowed. Rather than removing the
     * code, it simply converts the parenthesis to
     * entities rendering the code un-executable.
     * so this: eval('some code')
     * becomes: eval&#40;'some code'&#41;
     */
    $str = preg_replace('#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si', "\\1\\2&#40;\\3&#41;", $str);

    /* Final clean up
     * This adds a bit of extra precaution in case
     * something got through the above filters
     */
    $str = $this->_do_never_allowed($str);

    /* Images are handled in a special way
     * - Essentially, we want to know that after all of the character
     * conversion is done whether any unwanted, likely XSS, code was found.
     * If not, we return TRUE, as the image is clean.
     * However, if the string post-conversion does not match the
     * string post-removal of XSS, then it fails, as there was unwanted XSS
     * code found and removed/changed during processing
     */
    if($is_image === TRUE) {
      return ($str == $converted_string)?TRUE:FALSE;
    }

    return $str;
  }

  /**
   * Random Hash for protecting URLs
   * @return string
   */
  public function xss_hash() {
    if($this->_xss_hash == '') {
      mt_srand();
      $this->_xss_hash = md5(time() + mt_rand(0, 1999999999));
    }
    return $this->_xss_hash;
  }

  /**
   * HTML Entities Decode
   * This function is a replacement for html_entity_decode()
   * The reason we are not using html_entity_decode() by itself is
   * because while it is not technically correct to leave out the
   * semicolon at the end of an entity most browsers will still interpret
   * the entity correctly. html_entity_decode() does not convert entities
   * without semicolons, so we are left with our own little solution here.
   *
   * @param   string
   * @param   string
   * @return  string
   */
  public function entity_decode($str, $charset='UTF-8') {
    if(stristr($str, '&') === FALSE) {
      return $str;
    }
    $str = html_entity_decode($str, ENT_COMPAT, $charset);
    $str = preg_replace('~&#x(0*[0-9a-f]{2,5})~ei', 'chr(hexdec("\\1"))', $str);
    return preg_replace('~&#([0-9]{2,4})~e', 'chr(\\1)', $str);
  }

  /**
   * Filename Security
   *
   * @param   string
   * @param   bool  
   * @return  string
   */
  public function sanitize_filename($str, $relative_path = FALSE) {
    $bad = array( "../", "<!--", "-->", "<",
                  ">", "'", '"', '&', '$', '#',
                  '{', '}', '[', ']', '=', ';',
                  '?', "%20", "%22", "%3c", "%253c",
                  "%3e", "%0e", "%28", "%29", "%2528",
                  "%26", "%24", "%3f", "%3b", "%3d"
    );

    if(!$relateive_path) {
      $bad[] = './';
      $bad[] = '/';
    }
    $str = remove_invisible_characters($str, FALSE);
    return stripslashes(str_replace($bad, '', $str));
  }

  /**
   * Compact Exploded Words
   * Callback function for xss_clean() to remove whitespace from
   * things like j a v a s c r i p t
   *
   * @param   type
   * @return  type
   */
  protected function _compact_exploded_words($matches) {
    return preg_replace('/\s+/s', '', $matches[1]).$matches[2];
  }

  /**
   * Remove Evil HTML Attributes (like eventhandlers and style)
   * Removes the evil attribute and either:
   *  - Everything up until a space
   *    For example, everything between the pipes:
   *    <a |style=document.write('hello');alert('world');| class=link>
   *  - Everything inside the quotes
   *    For example, everything between the pipes:
   *    <a |style="document.write('hello'); alert('world');"| class="link">
   *
   * @param string $str The string to check
   * @param boolean $is_image TRUE if this is an image
   * @return string The string with the evil attributes removed
   */
  protected function _remove_evil_attributes($str, $is_image) {
    // All javascript event handlers (e.g. onload, onclick, onmouseover), style, and xmlns
    $evil_attributes = array('on\w*', 'style', 'xmlns', 'formaction');
    if($is_image===TRUE) {
      /* Adobe Photoshop puts XML metadata into JFIF images,
       * including namespacing, so we have to allow this for images.
       */
      unset($evil_attributes[array_search('xmlns', $evil_attributes)]);
    }
    do {
      $count = 0;
      $attribs = array();
      // Find occurrences of illegal attribute string with quotes (042 and 047 are octal quotes)
preg_match_all('/('.implode('|', $evil_attributes).')\s*=\s*(\042|\047)([^\\2]*?)(\\2)/is', $str, $matches, PREG_SET_ORDER);

      foreach ($matches as $attr) {
        $attribs[] = preg_quote($attr[0], '/');
      }

      // find occurrences of illegal attribute strings without quotes
      preg_match_all('/('.implode('|', $evil_attributes).')\s*=\s*([^\s>]*)/is', $str, $matches, PREG_SET_ORDER);

      foreach ($matches as $attr) {
        $attribs[] = preg_quote($attr[0], '/');
      }

      // replace illegal attribute strings that are inside an html tag
      if (count($attribs) > 0) {
        $str = preg_replace('/(<?)(\/?[^><]+?)([^A-Za-z<>\-])(.*?)('.implode('|', $attribs).')(.*?)([\s><]?)([><]*)/i', '$1$2 $4$6$7$8', $str, -1, $count);
      }
    } while($count);

    return $str;
  }

  /**
   * Sanitize Naughty HTML
   * Callback function for xss_clean() to remove naughty HTML elements
   *
   * @param array
   * @return  string
   */
  protected function _sanitize_naughty_html($matches) {
    // encode opening brace
    $str = '&lt;'.$matches[1].$matches[2].$matches[3];

    // encode captured opening or closing brace to prevent recursive vectors
    $str .= str_replace(array('>', '<'), array('&gt;', '&lt;'),
              $matches[4]);
    return $str;
  }

  /**
   * JS Link Removal
   * Callback function for xss_clean() to sanitize links
   * This limits the PCRE backtracks, making it more performance friendly
   * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
   * PHP 5.2+ on link-heavy strings
   *
   * @param array
   * @return  string
   */
  protected function _js_link_removal($match) {
    return str_replace(
      $match[1],
      preg_replace(
        '#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|data\s*:)#si',
        '',
        $this->_filter_attributes(str_replace(array('<', '>'), '', $match[1]))
      ),
      $match[0]
    );
  }

  /**
   * JS Image Removal
   * Callback function for xss_clean() to sanitize image tags
   * This limits the PCRE backtracks, making it more performance friendly
   * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
   * PHP 5.2+ on image tag heavy strings
   *
   * @param array
   * @return  string
   */
  protected function _js_img_removal($match) {
    return str_replace(
      $match[1],
      preg_replace(
        '#src=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si',
        '',
        $this->_filter_attributes(str_replace(array('<', '>'), '', $match[1]))
      ),
      $match[0]
    );
  }

  /**
   * Attribute Conversion
   * Used as a callback for XSS Clean
   *
   * @param array
   * @return  string
   */
  protected function _convert_attribute($match) {
    return str_replace(array('>', '<', '\\'), array('&gt;', '&lt;', '\\\\'), $match[0]);
  }

  /**
   * Filter Attributes
   * Filters tag attributes for consistency and safety
   *
   * @param string
   * @return  string
   */
  protected function _filter_attributes($str) {
    $out = '';

    if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches)) {
      foreach ($matches[0] as $match) {
        $out .= preg_replace("#/\*.*?\*/#s", '', $match);
      }
    }

    return $out;
  }

  /**
   * HTML Entity Decode Callback
   * Used as a callback for XSS Clean
   *
   * @param array
   * @return  string
   */
  protected function _decode_entity($match) {
    return $this->entity_decode($match[0], strtoupper(config_item('charset')));
  }

  /**
   * Validate URL entities
   * Called by xss_clean()
   *
   * @param   string
   * @return  string
   */
  protected function _validate_entities($str) {
    /* Protect GET variables in URLs */
     // 901119URL5918AMP18930PROTECT8198
    $str = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-]+)|i', $this->xss_hash()."\\1=\\2", $str);
    /* Validate standard character entities
     * Add a semicolon if missing.  We do this to enable
     * the conversion of entities to ASCII later.
     */
    $str = preg_replace('#(&\#?[0-9a-z]{2,})([\x00-\x20])*;?#i', "\\1;\\2", $str);
    /* Validate UTF16 two byte encoding (x00)
     * Just as above, adds a semicolon if missing.
     */
    $str = preg_replace('#(&\#x?)([0-9A-F]+);?#i',"\\1\\2;",$str);
    /* Un-Protect GET variables in URLs */
    $str = str_replace($this->xss_hash(), '&', $str);

    return $str;
  }

  /**
   * Do Never Allowed
   * A utility function for xss_clean()
   *
   * @param   string
   * @return  string
   */
  protected function _do_never_allowed($str) {
    $str = str_replace(array_keys($this->_never_allowed_str), $this->_never_allowed_str, $str);
    foreach ($this->_never_allowed_regex as $regex) {
      $str = preg_replace('#'.$regex.'#is', '[removed]', $str);
    }
    return $str;
  }

  /**
   * Set Cross Site Request Forgery Protection Cookie
   *
   * @return  string
   */
  protected function _csrf_set_hash() {
    if ($this->_csrf_hash == '') {
      // If the cookie exists we will use it's value.
      // We don't necessarily want to regenerate it with
      // each page load since a page could contain embedded
      // sub-pages causing this feature to fail
      if (isset($_COOKIE[$this->_csrf_cookie_name]) &&
        preg_match('#^[0-9a-f]{32}$#iS', $_COOKIE[$this->_csrf_cookie_name]) === 1) {
        return $this->_csrf_hash = $_COOKIE[$this->_csrf_cookie_name];
      }

      return $this->_csrf_hash = md5(uniqid(rand(), TRUE));
    }
    return $this->_csrf_hash;
  }
}