CodeIgniter.php 引入的第八个核心文件($SEC)。

虽然对 xss csrf 有一点了解和运用,但安全相关源码时依然有些懵,一方面说明基础不过扎实,另一方面也说明心要更加静一点。

文档地址

知识点

正则

命名子组

在 PHP 4.3.3 中,可以对子组使用 (?P<name>pattern) 的语法进行命名。
这个子模式将会在匹配结果中同时以其名称和顺序(数字下标)出现, PHP 5.2.2中又增加了两种味子组命名的语法:
(?<name>pattern)(?’name’pattern)

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<?php
$a = '</ blink>';
$pattern = '#<(?<slash>/*\s*)(?<tagName>[a-z0-9]+)(?=[^a-z0-9]|$)#isS';
preg_match($pattern, $a, $match);
var_dump($match);

参考资料

流程

xss_clean

  1. 如果是数组则递归处理内容
  2. 移除ACSII中的控制字符(16进制、url转义格式)。
  3. 解码 URL编码(rawurldecode),eg:%11
  4. 转义 < 等危险符号。但这里有些疑问
  5. 制表符转为空格,eg:ja vascript
  6. 移除不允许字符
  7. 处理 <? 等违规字符。这里有疑问
  8. 处理违法单词如 javascript、expression等。
  9. 移除危险的超链接

源代码

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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 - 2015, 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. (http://ellislab.com/)
* @copyright Copyright (c) 2014 - 2015, British Columbia Institute of Technology (http://bcit.ca/)
* @license http://opensource.org/licenses/MIT MIT License
* @link http://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 http://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.write' => '[removed]',
'.parentNode' => '[removed]',
'.innerHTML' => '[removed]',
'-moz-binding' => '[removed]',
'<!--' => '&lt;!--',
'-->' => '--&gt;',
'<![CDATA[' => '&lt;![CDATA[',
'<comment>' => '&lt;comment&gt;'
);

/**
* List of never allowed regex replacements
*
* @var array
*/
protected $_never_allowed_regex = array(
'javascript\s*:',
'(document|(document\.)?window)\.(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
// 获取配置中的 csrf 配置
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 增加前缀
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')
{
// 如果不是 POST 操作只生成csrf
return $this->csrf_set_cookie();
}

// csrf 校验白名单
// 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;
}
}
}

// post 和 cookie 中必须包含设定好相等的随机值
// Do the tokens exist in both the _POST and _COOKIE arrays?
if ( ! isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])
OR $_POST[$this->_csrf_token_name] !== $_COOKIE[$this->_csrf_cookie_name]) // Do the tokens match?
{
$this->csrf_show_error();
}

// 校验通过清除数据
// We kill this since we're done and we don't want to polute the _POST array
unset($_POST[$this->_csrf_token_name]);

// 是否每次提交都重新生成?
// 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();

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))
{
while (list($key) = each($str))
{
$str[$key] = $this->xss_clean($str[$key]);
}

return $str;
}

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

/*
* URL Decode
* 对已编码的 URL 字符串进行解码
*
* 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
*/
do
{
$str = rawurldecode($str);
}
while (preg_match('/%[0-9a-f]{2,}/i', $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.
*/
//<img='http://xss.org/m.js'> s 将字符串视为单行,换行符作为普通字符. i模式中的字符将同时匹配大小写字母.
$str = preg_replace_callback("/[^a-z0-9>]+[a-z0-9]+=([\'\"]).*?\\1/si", array($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))
{
$str = preg_replace_callback('#<a[^a-z0-9>]+([^>]*?)(?:>|$)#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
* 让 html 元素无害
*
* If a tag containing any of the words in the list
* below is found, the tag gets converted to entities.
*
* So this: <blink>
* Becomes: &lt;blink&gt;
*/
$pattern = '#'
.'<((?<slash>/*\s*)(?<tagName>[a-z0-9]+)(?=[^a-z0-9]|$)' // 命名子组 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);

// echo $str;
// var_dump(htmlspecialchars($str));
// die('sss');

/*
* 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&#40;'some code'&#41;
*/
$str = preg_replace(
'#(alert|prompt|confirm|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 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;
}

// 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;

do
{
$str_compare = $str;

// Decode standard entities, avoiding false positives
if (preg_match_all('/&[a-z]{2,}(?![a-z;])/i', $str, $matches))
{
if ( ! isset($_entities))
{
$_entities = array_map(
'strtolower',
is_php('5.3.4')
? get_html_translation_table(HTML_ENTITIES, $flag, $charset)
: get_html_translation_table(HTML_ENTITIES, $flag)
);

// If we're not on PHP 5.4+, add the possibly dangerous HTML 5
// entities to the array manually
if ($flag === ENT_COMPAT)
{
$_entities[':'] = '&colon;';
$_entities['('] = '&lpar;';
$_entities[')'] = '&rpar;';
$_entities["\n"] = '&newline;';
$_entities["\t"] = '&tab;';
}
}

$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;
}
}

$str = str_ireplace(array_keys($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,
$charset
);
}
while ($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*["\'](.+?)["\'].*?\>#', '#<img[\s/]+.*?src\s*=\s*(.+?).*?\>#'), '\\1', $str);
}

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

/**
* 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', '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($matches['closeTag']))
{
return '&lt;'.$matches[1];
}
// Is the element that we caught naughty? If so, escape it
elseif (in_array(strtolower($matches['tagName']), $naughty_tags, TRUE))
{
return '&lt;'.$matches[1].'&gt;';
}
// For other tags, see if their attributes are "evil" and strip those
elseif (isset($matches['attributes']))
{
// We'll need to catch all attributes separately first
$pattern = '#'
.'([\s\042\047/=]*)' // non-attribute characters, excluding > (tag close) for obvious reasons
.'(?<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';

if ($count = preg_match_all($pattern, $matches['attributes'], $attributes, PREG_SET_ORDER | PREG_OFFSET_CAPTURE))
{
// Since we'll be using substr_replace() below, we
// need to handle the attributes in reverse order,
// so we don't damage the string.
for ($i = $count - 1; $i > -1; $i--)
{
if (
// Is it indeed an "evil" attribute?
preg_match('#^('.implode('|', $evil_attributes).')$#i', $attributes[$i]['name'][0])
// Or an attribute not starting with a letter? Some parsers get confused by that
OR ! ctype_alpha($attributes[$i]['name'][0][0])
// Does it have an equals sign, but no value and not quoted? Strip that too!
OR (trim($attributes[$i]['value'][0]) === '')
)
{
$matches['attributes'] = substr_replace(
$matches['attributes'],
' [removed]',
$attributes[$i][0][1],
strlen($attributes[$i][0][0])
);
}
}

// Note: This will strip some non-space characters and/or
// reduce multiple spaces between attributes.
return '<'.$matches['slash'].$matches['tagName'].' '.trim($matches['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;)|javascript:|livescript:|mocha:|charset=|window\.|document\.|\.cookie|<script|<xss|data\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;)|javascript:|livescript:|mocha:|charset=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si',
'',
$this->_filter_attributes($match[1])
),
$match[0]
);
}

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

/**
* Attribute Conversion
* //转义
*
* @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
*
* Filters tag attributes for consistency and safety.
*
* @used-by CI_Security::_js_img_removal()
* @used-by CI_Security::_js_link_removal()
* @param string $str
* @return string
*/
protected function _filter_attributes($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-by CI_Security::xss_clean()
* @param array $match
* @return string
*/
protected function _decode_entity($match)
{
// Protect GET variables in URLs
// 901119URL5918AMP18930PROTECT8198
$match = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-/]+)|i', $this->xss_hash().'\\1=\\2', $match[0]);
// Decode, then un-protect URL GET vars
return str_replace(
$this->xss_hash(),
'&',
$this->entity_decode($match, $this->charset)
);
}

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

/**
* Do Never Allowed
*
* @used-by CI_Security::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 CSRF Hash and Cookie
* 保存 cookie 和对象中的随机值
*
* @return string
*/
protected function _csrf_set_hash()
{
if ($this->_csrf_hash === NULL)
{
// If the cookie exists we will use its 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

// 检测 存在于cookie中随机值的格式(32位字母数字)。
if (isset($_COOKIE[$this->_csrf_cookie_name]) && is_string($_COOKIE[$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];
}

//没有则重新生成
$rand = $this->get_random_bytes(16);
$this->_csrf_hash = ($rand === FALSE)
? md5(uniqid(mt_rand(), TRUE))
: bin2hex($rand);
}

return $this->_csrf_hash;
}

}