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<?php

/**

 * CodeIgniter

 *

 * An open source application development framework for PHP

 *

 * This content is released under the MIT License (MIT)

 *

 * Copyright (c) 2014 - 2018, British Columbia Institute of Technology

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

 * THE SOFTWARE.

 *

 * @package	CodeIgniter

 * @author	EllisLab Dev Team

 * @copyright	Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)

 * @copyright	Copyright (c) 2014 - 2018, British Columbia Institute of Technology (http://bcit.ca/)

 * @license	http://opensource.org/licenses/MIT	MIT License

 * @link	https://codeigniter.com

 * @since	Version 1.0.0

 * @filesource

 */

defined('BASEPATH') OR exit('No direct script access allowed');

/**

 * Security Class

 *

 * @package		CodeIgniter

 * @subpackage	Libraries

 * @category	Security

 * @author		EllisLab Dev Team

 * @link		https://codeigniter.com/user_guide/libraries/security.html

 */

class CI_Security {

	/**

	 * List of sanitize filename strings

	 *

	 * @var	array

	 */

	public $filename_bad_chars =	array(

		'../', '<!--', '-->', '<', '>',

		"'", '"', '&', '$', '#',

		'{', '}', '[', ']', '=',

		';', '?', '%20', '%22',

		'%3c',		// <

		'%253c',	// <

		'%3e',		// >

		'%0e',		// >

		'%28',		// (

		'%29',		// )

		'%2528',	// (

		'%26',		// &

		'%24',		// $

		'%3f',		// ?

		'%3b',		// ;

		'%3d'		// =

	);

	/**

	 * Character set

	 *

	 * Will be overridden by the constructor.

	 *

	 * @var	string

	 */

	public $charset = 'UTF-8';

	/**

	 * XSS Hash

	 *

	 * Random Hash for protecting URLs.

	 *

	 * @var	string

	 */

	protected $_xss_hash;

	/**

	 * CSRF Hash

	 *

	 * Random hash for Cross Site Request Forgery protection cookie

	 *

	 * @var	string

	 */

	protected $_csrf_hash;

	/**

	 * CSRF Expire time

	 *

	 * Expiration time for Cross Site Request Forgery protection cookie.

	 * Defaults to two hours (in seconds).

	 *

	 * @var	int

	 */

	protected $_csrf_expire =	7200;

	/**

	 * CSRF Token name

	 *

	 * Token name for Cross Site Request Forgery protection cookie.

	 *

	 * @var	string

	 */

	protected $_csrf_token_name =	'ci_csrf_token';

	/**

	 * CSRF Cookie name

	 *

	 * Cookie name for Cross Site Request Forgery protection cookie.

	 *

	 * @var	string

	 */

	protected $_csrf_cookie_name =	'ci_csrf_token';

	/**

	 * List of never allowed strings

	 *

	 * @var	array

	 */

	protected $_never_allowed_str =	array(

		'document.cookie' => '[removed]',

		'(document).cookie' => '[removed]',

		'document.write'  => '[removed]',

		'(document).write'  => '[removed]',

		'.parentNode'     => '[removed]',

		'.innerHTML'      => '[removed]',

		'-moz-binding'    => '[removed]',

		'<!--'            => '&lt;!--',

		'-->'             => '-->',

		'<![CDATA['       => '&lt;![CDATA[',

		'<comment>'	  => '&lt;comment&gt;',

		'<%'              => '&lt;&#37;'

	);

	/**

	 * List of never allowed regex replacements

	 *

	 * @var	array

	 */

	protected $_never_allowed_regex = array(

		'javascript\s*:',

		'(\(?document\)?|\(?window\)?(\.document)?)\.(location|on\w*)',

		'expression\s*(\(|&\#40;)', // CSS and IE

		'vbscript\s*:', // IE, surprise!

		'wscript\s*:', // IE

		'jscript\s*:', // IE

		'vbs\s*:', // IE

		'Redirect\s+30\d',

		"([\"'])?data\s*:[^\\1]*?base64[^\\1]*?,[^\\1]*?\\1?"

	);

	/**

	 * Class constructor

	 *

	 * @return	void

	 */

	public function __construct()

	{

		// Is CSRF protection enabled?

		if (config_item('csrf_protection'))

		{

			// CSRF config

			foreach (array('csrf_expire', 'csrf_token_name', 'csrf_cookie_name') as $key)

			{

				if (NULL !== ($val = config_item($key)))

				{

					$this->{'_'.$key} = $val;

				}

			}

			// Append application specific cookie prefix

			if ($cookie_prefix = config_item('cookie_prefix'))

			{

				$this->_csrf_cookie_name = $cookie_prefix.$this->_csrf_cookie_name;

			}

			// Set the CSRF hash

			$this->_csrf_set_hash();

		}

		$this->charset = strtoupper(config_item('charset'));

		log_message('info', 'Security Class Initialized');

	}

	// --------------------------------------------------------------------

	/**

	 * CSRF Verify

	 *

	 * @return	CI_Security

	 */

	public function csrf_verify()

	{

		// If it's not a POST request we will set the CSRF cookie

		if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST')

		{

			return $this->csrf_set_cookie();

		}

		// Check if URI has been whitelisted from CSRF checks

		if ($exclude_uris = config_item('csrf_exclude_uris'))

		{

			$uri = load_class('URI', 'core');

			foreach ($exclude_uris as $excluded)

			{

				if (preg_match('#^'.$excluded.'$#i'.(UTF8_ENABLED ? 'u' : ''), $uri->uri_string()))

				{

					return $this;

				}

			}

		}

		// Check CSRF token validity, but don't error on mismatch just yet - we'll want to regenerate

		$valid = isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])

			&& hash_equals($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]);

		// We kill this since we're done and we don't want to pollute the _POST array

		unset($_POST[$this->_csrf_token_name]);

		// Regenerate on every submission?

		if (config_item('csrf_regenerate'))

		{

			// Nothing should last forever

			unset($_COOKIE[$this->_csrf_cookie_name]);

			$this->_csrf_hash = NULL;

		}

		$this->_csrf_set_hash();

		$this->csrf_set_cookie();

		if ($valid !== TRUE)

		{

			$this->csrf_show_error();

		}

		log_message('info', 'CSRF token verified');

		return $this;

	}

	// --------------------------------------------------------------------

	/**

	 * CSRF Set Cookie

	 *

	 * @codeCoverageIgnore

	 * @return	CI_Security

	 */

	public function csrf_set_cookie()

	{

		$expire = time() + $this->_csrf_expire;

		$secure_cookie = (bool) config_item('cookie_secure');

		if ($secure_cookie && ! is_https())

		{

			return FALSE;

		}

		setcookie(

			$this->_csrf_cookie_name,

			$this->_csrf_hash,

			$expire,

			config_item('cookie_path'),

			config_item('cookie_domain'),

			$secure_cookie,

			config_item('cookie_httponly')

		);

		log_message('info', 'CSRF cookie sent');

		return $this;

	}

	// --------------------------------------------------------------------

	/**

	 * Show CSRF Error

	 *

	 * @return	void

	 */

	public function csrf_show_error()

	{

		show_error('The action you have requested is not allowed.', 403);

	}

	// --------------------------------------------------------------------

	/**

	 * Get CSRF Hash

	 *

	 * @see		CI_Security::$_csrf_hash

	 * @return 	string	CSRF hash

	 */

	public function get_csrf_hash()

	{

		return $this->_csrf_hash;

	}

	// --------------------------------------------------------------------

	/**

	 * Get CSRF Token Name

	 *

	 * @see		CI_Security::$_csrf_token_name

	 * @return	string	CSRF token name

	 */

	public function get_csrf_token_name()

	{

		return $this->_csrf_token_name;

	}

	// --------------------------------------------------------------------

	/**

	 * XSS Clean

	 *

	 * Sanitizes data so that Cross Site Scripting Hacks can be

	 * prevented.  This method 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: Should only be used to deal with data upon submission.

	 *	 It's not something that should be used for general

	 *	 runtime processing.

	 *

	 * @link	http://channel.bitflux.ch/wiki/XSS_Prevention

	 * 		Based in part on some code and ideas from Bitflux.

	 *

	 * @link	http://ha.ckers.org/xss.html

	 * 		To help develop this script I used this great list of

	 *		vulnerabilities along with a few other hacks I've

	 *		harvested from examining vulnerabilities in other programs.

	 *

	 * @param	string|string[]	$str		Input data

	 * @param 	bool		$is_image	Whether the input is an image

	 * @return	string

	 */

	public function xss_clean($str, $is_image = FALSE)

	{

		// Is the string an array?

		if (is_array($str))

		{

			foreach ($str as $key => &$value)

			{

				$str[$key] = $this->xss_clean($value);

			}

			return $str;

		}

		// Remove Invisible Characters

		$str = remove_invisible_characters($str);

		/*

		 * URL Decode

		 *

		 * Just in case stuff like this is submitted:

		 *

		 * <a href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a>

		 *

		 * Note: Use rawurldecode() so it does not remove plus signs

		 */

		if (stripos($str, '%') !== false)

		{

			do

			{

				$oldstr = $str;

				$str = rawurldecode($str);

				$str = preg_replace_callback('#%(?:\s*[0-9a-f]){2,}#i', array($this, '_urldecodespaces'), $str);

			}

			while ($oldstr !== $str);

			unset($oldstr);

		}

		/*

		 * 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.

		 */

		$str = preg_replace_callback("/[^a-z0-9>]+[a-z0-9]+=([\'\"]).*?\\1/si", array($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.

		 */

		$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', 'jscript', 'wscript',

			'vbs', 'script', 'base64', 'applet', 'alert', 'document',

			'write', 'cookie', 'window', 'confirm', 'prompt', 'eval'

		);

		foreach ($words as $word)

		{

			$word = implode('\s*', str_split($word)).'\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"

			$str = preg_replace_callback('#('.substr($word, 0, -3).')(\W)#is', array($this, '_compact_exploded_words'), $str);

		}

		/*

		 * Remove disallowed Javascript in links or img tags

		 * We used to do some version comparisons and use of stripos(),

		 * but it is dog slow compared to these simplified non-capturing

		 * preg_match(), especially if the pattern exists in the string

		 *

		 * Note: It was reported that not only space characters, but all in

		 * the following pattern can be parsed as separators between a tag name

		 * and its attributes: [\d\s"\'`;,\/\=\(\x00\x0B\x09\x0C]

		 * ... however, remove_invisible_characters() above already strips the

		 * hex-encoded ones, so we'll skip them below.

		 */

		do

		{

			$original = $str;

			if (preg_match('/<a/i', $str))

			{

				$str = preg_replace_callback('#<a(?:rea)?[^a-z0-9>]+([^>]*?)(?:>|$)#si', array($this, '_js_link_removal'), $str);

			}

			if (preg_match('/<img/i', $str))

			{

				$str = preg_replace_callback('#<img[^a-z0-9]+([^>]*?)(?:\s?/?>|$)#si', array($this, '_js_img_removal'), $str);

			}

			if (preg_match('/script|xss/i', $str))

			{

				$str = preg_replace('#</*(?:script|xss).*?>#si', '[removed]', $str);

			}

		}

		while ($original !== $str);

		unset($original);

		/*

		 * 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>

		 * Becomes: <blink>

		 */

		$pattern = '#'

			.'<((?<slash>/*\s*)((?<tagName>[a-z0-9]+)(?=[^a-z0-9]|$)|.+)' // tag start and name, followed by a non-tag character

			.'[^\s\042\047a-z0-9>/=]*' // a valid attribute character immediately after the tag would count as a separator

			// optional attributes

			.'(?<attributes>(?:[\s\042\047/=]*' // non-attribute characters, excluding > (tag close) for obvious reasons

			.'[^\s\042\047>/=]+' // attribute characters

			// optional attribute-value

				.'(?:\s*=' // attribute-value separator

					.'(?:[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*))' // single, double or non-quoted value

				.')?' // end optional attribute-value group

			.')*)' // end optional attributes group

			.'[^>]*)(?<closeTag>\>)?#isS';

		// Note: It would be nice to optimize this for speed, BUT

		//       only matching the naughty elements here results in

		//       false positives and in turn - vulnerabilities!

		do

		{

			$old_str = $str;

			$str = preg_replace_callback($pattern, array($this, '_sanitize_naughty_html'), $str);

		}

		while ($old_str !== $str);

		unset($old_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.

		 *

		 * For example:	eval('some code')

		 * Becomes:	eval('some code')

		 */

		$str = preg_replace(

			'#(alert|prompt|confirm|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si',

			'\\1\\2(\\3)',

			$str

		);

		// Same thing, but for "tag functions" (e.g. eval`some code`)

		// See https://github.com/bcit-ci/CodeIgniter/issues/5420

		$str = preg_replace(

			'#(alert|prompt|confirm|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)`(.*?)`#si',

			'\\1\\2`\\3`',

			$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 matched 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);

		}

		return $str;

	}

	// --------------------------------------------------------------------

	/**

	 * XSS Hash

	 *

	 * Generates the XSS hash if needed and returns it.

	 *

	 * @see		CI_Security::$_xss_hash

	 * @return	string	XSS hash

	 */

	public function xss_hash()

	{

		if ($this->_xss_hash === NULL)

		{

			$rand = $this->get_random_bytes(16);

			$this->_xss_hash = ($rand === FALSE)

				? md5(uniqid(mt_rand(), TRUE))

				: bin2hex($rand);

		}

		return $this->_xss_hash;

	}

	// --------------------------------------------------------------------

	/**

	 * Get random bytes

	 *

	 * @param	int	$length	Output length

	 * @return	string

	 */

	public function get_random_bytes($length)

	{

		if (empty($length) OR ! ctype_digit((string) $length))

		{

			return FALSE;

		}

		if (function_exists('random_bytes'))

		{

			try

			{

				// The cast is required to avoid TypeError

				return random_bytes((int) $length);

			}

			catch (Exception $e)

			{

				// If random_bytes() can't do the job, we can't either ...

				// There's no point in using fallbacks.

				log_message('error', $e->getMessage());

				return FALSE;

			}

		}

		// Unfortunately, none of the following PRNGs is guaranteed to exist ...

		if (defined('MCRYPT_DEV_URANDOM') && ($output = mcrypt_create_iv($length, MCRYPT_DEV_URANDOM)) !== FALSE)

		{

			return $output;

		}

		if (is_readable('/dev/urandom') && ($fp = fopen('/dev/urandom', 'rb')) !== FALSE)

		{

			// Try not to waste entropy ...

			is_php('5.4') && stream_set_chunk_size($fp, $length);

			$output = fread($fp, $length);

			fclose($fp);

			if ($output !== FALSE)

			{

				return $output;

			}

		}

		if (function_exists('openssl_random_pseudo_bytes'))

		{

			return openssl_random_pseudo_bytes($length);

		}

		return FALSE;

	}

	// --------------------------------------------------------------------

	/**

	 * HTML Entities Decode

	 *

	 * 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. Bummer.

	 *

	 * @link	http://php.net/html-entity-decode

	 *

	 * @param	string	$str		Input

	 * @param	string	$charset	Character set

	 * @return	string

	 */

	public function entity_decode($str, $charset = NULL)

	{

		if (strpos($str, '&') === FALSE)

		{

			return $str;

		}

		static $_entities;

		isset($charset) OR $charset = $this->charset;

		$flag = is_php('5.4')

			? ENT_COMPAT | ENT_HTML5

			: ENT_COMPAT;

		if ( ! isset($_entities))

		{

			$_entities = array_map('strtolower', get_html_translation_table(HTML_ENTITIES, $flag, $charset));

			// If we're not on PHP 5.4+, add the possibly dangerous HTML 5

			// entities to the array manually

			if ($flag === ENT_COMPAT)

			{

				$_entities[':'] = ':';

				$_entities['('] = '(';

				$_entities[')'] = ')';

				$_entities["\n"] = '
';

				$_entities["\t"] = '	';

			}

		}

		do

		{

			$str_compare = $str;

			// Decode standard entities, avoiding false positives

			if (preg_match_all('/&[a-z]{2,}(?![a-z;])/i', $str, $matches))

			{

				$replace = array();

				$matches = array_unique(array_map('strtolower', $matches[0]));

				foreach ($matches as &$match)

				{

					if (($char = array_search($match.';', $_entities, TRUE)) !== FALSE)

					{

						$replace[$match] = $char;

					}

				}

				$str = str_replace(array_keys($replace), array_values($replace), $str);

			}

			// Decode numeric & UTF16 two byte entities

			$str = html_entity_decode(

				preg_replace('/(&#(?:x0*[0-9a-f]{2,5}(?![0-9a-f;])|(?:0*\d{2,4}(?![0-9;]))))/iS', '$1;', $str),

				$flag,

				$charset

			);

			if ($flag === ENT_COMPAT)

			{

				$str = str_replace(array_values($_entities), array_keys($_entities), $str);

			}

		}

		while ($str_compare !== $str);

		return $str;

	}

	// --------------------------------------------------------------------

	/**

	 * Sanitize Filename

	 *

	 * @param	string	$str		Input file name

	 * @param 	bool	$relative_path	Whether to preserve paths

	 * @return	string

	 */

	public function sanitize_filename($str, $relative_path = FALSE)

	{

		$bad = $this->filename_bad_chars;

		if ( ! $relative_path)

		{

			$bad[] = './';

			$bad[] = '/';

		}

		$str = remove_invisible_characters($str, FALSE);

		do

		{

			$old = $str;

			$str = str_replace($bad, '', $str);

		}

		while ($old !== $str);

		return stripslashes($str);

	}

	// ----------------------------------------------------------------

	/**

	 * Strip Image Tags

	 *

	 * @param	string	$str

	 * @return	string

	 */

	public function strip_image_tags($str)

	{

		return preg_replace(

			array(

				'#<img[\s/]+.*?src\s*=\s*(["\'])([^\\1]+?)\\1.*?\>#i',

				'#<img[\s/]+.*?src\s*=\s*?(([^\s"\'=<>`]+)).*?\>#i'

			),

			'\\2',

			$str

		);

	}

	// ----------------------------------------------------------------

	/**

	 * URL-decode taking spaces into account

	 *

	 * @see		https://github.com/bcit-ci/CodeIgniter/issues/4877

	 * @param	array	$matches

	 * @return	string

	 */

	protected function _urldecodespaces($matches)

	{

		$input    = $matches[0];

		$nospaces = preg_replace('#\s+#', '', $input);

		return ($nospaces === $input)

			? $input

			: rawurldecode($nospaces);

	}

	// ----------------------------------------------------------------

	/**

	 * Compact Exploded Words

	 *

	 * Callback method for xss_clean() to remove whitespace from

	 * things like 'j a v a s c r i p t'.

	 *

	 * @used-by	CI_Security::xss_clean()

	 * @param	array	$matches

	 * @return	string

	 */

	protected function _compact_exploded_words($matches)

	{

		return preg_replace('/\s+/s', '', $matches[1]).$matches[2];

	}

	// --------------------------------------------------------------------

	/**

	 * Sanitize Naughty HTML

	 *

	 * Callback method for xss_clean() to remove naughty HTML elements.

	 *

	 * @used-by	CI_Security::xss_clean()

	 * @param	array	$matches

	 * @return	string

	 */

	protected function _sanitize_naughty_html($matches)

	{

		static $naughty_tags    = array(

			'alert', 'area', 'prompt', 'confirm', 'applet', 'audio', 'basefont', 'base', 'behavior', 'bgsound',

			'blink', 'body', 'embed', 'expression', 'form', 'frameset', 'frame', 'head', 'html', 'ilayer',

			'iframe', 'input', 'button', 'select', 'isindex', 'layer', 'link', 'meta', 'keygen', 'object',

			'plaintext', 'style', 'script', 'textarea', 'title', 'math', 'video', 'svg', 'xml', 'xss'

		);

		static $evil_attributes = array(

			'on\w+', 'style', 'xmlns', 'formaction', 'form', 'xlink:href', 'FSCommand', 'seekSegmentTime'

		);

		// First, escape unclosed tags

		if (empty($matches['closeTag']))

		{

			return '<'.$matches[1];

		}

		// Is the element that we caught naughty? If so, escape it

		elseif (in_array(strtolower($matches['tagName']), $naughty_tags, TRUE))

		{

			return '<'.$matches[1].'>';

		}

		// For other tags, see if their attributes are "evil" and strip those

		elseif (isset($matches['attributes']))

		{

			// We'll store the already filtered attributes here

			$attributes = array();

			// Attribute-catching pattern

			$attributes_pattern = '#'

				.'(?<name>[^\s\042\047>/=]+)' // attribute characters

				// optional attribute-value

				.'(?:\s*=(?<value>[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*)))' // attribute-value separator

				.'#i';

			// Blacklist pattern for evil attribute names

			$is_evil_pattern = '#^('.implode('|', $evil_attributes).')$#i';

			// Each iteration filters a single attribute

			do

			{

				// Strip any non-alpha characters that may precede an attribute.

				// Browsers often parse these incorrectly and that has been a

				// of numerous XSS issues we've had.

				$matches['attributes'] = preg_replace('#^[^a-z]+#i', '', $matches['attributes']);

				if ( ! preg_match($attributes_pattern, $matches['attributes'], $attribute, PREG_OFFSET_CAPTURE))

				{

					// No (valid) attribute found? Discard everything else inside the tag

					break;

				}

				if (

					// Is it indeed an "evil" attribute?

					preg_match($is_evil_pattern, $attribute['name'][0])

					// Or does it have an equals sign, but no value and not quoted? Strip that too!

					OR (trim($attribute['value'][0]) === '')

				)

				{

					$attributes[] = 'xss=removed';

				}

				else

				{

					$attributes[] = $attribute[0][0];

				}

				$matches['attributes'] = substr($matches['attributes'], $attribute[0][1] + strlen($attribute[0][0]));

			}

			while ($matches['attributes'] !== '');

			$attributes = empty($attributes)

				? ''

				: ' '.implode(' ', $attributes);

			return '<'.$matches['slash'].$matches['tagName'].$attributes.'>';

		}

		return $matches[0];

	}

	// --------------------------------------------------------------------

	/**

	 * JS Link Removal

	 *

	 * Callback method 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.

	 *

	 * @used-by	CI_Security::xss_clean()

	 * @param	array	$match

	 * @return	string

	 */

	protected function _js_link_removal($match)

	{

		return str_replace(

			$match[1],

			preg_replace(

				'#href=.*?(?:(?:alert|prompt|confirm)(?:\(|&\#40;|`|&\#96;)|javascript:|livescript:|mocha:|charset=|window\.|\(?document\)?\.|\.cookie|<script|<xss|d\s*a\s*t\s*a\s*:)#si',

				'',

				$this->_filter_attributes($match[1])

			),

			$match[0]

		);

	}

	// --------------------------------------------------------------------

	/**

	 * JS Image Removal

	 *

	 * Callback method 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.

	 *

	 * @used-by	CI_Security::xss_clean()

	 * @param	array	$match

	 * @return	string

	 */

	protected function _js_img_removal($match)

	{

		return str_replace(

			$match[1],

			preg_replace(

				'#src=.*?(?:(?:alert|prompt|confirm|eval)(?:\(|&\#40;|`|&\#96;)|javascript:|livescript:|mocha:|charset=|window\.|\(?document\)?\.|\.cookie|<script|<xss|base64\s*,)#si',

				'',

				$this->_filter_attributes($match[1])

			),

			$match[0]

		);

	}

	// --------------------------------------------------------------------

	/**

	 * Attribute Conversion

	 *

	 * @used-by	CI_Security::xss_clean()

	 * @param	array	$match

	 * @return	string

	 */

	protected function _convert_attribute($match)

	{

		return str_replace(array('>', '<', '\\'), array('&gt;', '&lt;', '\\\\'), $match[0]);

	}

	// --------------------------------------------------------------------

	/**

	 * Filter Attributes