本文深入剖析了CI框架中的安全组件，重点介绍了其核心方法xss_clean的工作原理及内部实现细节，包括实体编码调整、HTML实体解码、关键词过滤等步骤。
Security 安全类主要是对 url 内容进行 xss 攻击的过滤
很多匹配格式 建议阅读之前先巩固下正则的知识
主要的 xss_clear 方法 其中的处理流程如下：
_validate_entities 对url进行实体编码的调整
_convert_attribute 对标签 属性=值 形式字符串中的 < > \ 字符进行实体转换
_decode_entity 对HTML实体解码 实体转换成字符 解决php函数不能解码10进制形式的HTML实体的问题（这里解码是为了更方便的对数据进行匹配处理）
_do_never_allowed 永远不允许的关键词 过滤掉
转义 <?php
_compact_exploded_words 将关键词中间的空格去除
do
_js_link_removel ->_filter_attributes
_js_img_removal ->_filter_attributes
标签里面的 属性 href src 中出现可执行脚本代码 将属性带代码一同干掉
filter_attributes 是去除里面的注释部分
while()
remove_evil_attributes 去除事件里面的脚本代码
_sanitize_naughty_html 对html中的编码实体化 （之前解码为了处理方便 处理完毕再编码到实体）
_do_never_allowed 同上
下面是源码and注释
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class CI_Security {
protected $_xss_hash = '';
protected $_csrf_hash = '';
protected $_csrf_expire = 7200;
protected $_csrf_token_name = 'ci_csrf_token';
protected $_csrf_cookie_name = 'ci_csrf_token';
//用 val 代替 key
protected $_never_allowed_str = array(
'document.cookie' => '[removed]',
'document.write' => '[removed]',
'.parentNode' => '[removed]',
'.innerHTML' => '[removed]',
'window.location' => '[removed]',
'-moz-binding' => '[removed]',
'<!--' => '<!--',
'-->' => '-->',
'<![CDATA[' => '<![CDATA[',
'<comment>' => '<comment>'
);
//用[removed]代替 key作为正则匹配到的部分
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?"
);
public function __construct()
{
if (config_item('csrf_protection') === TRUE)
{
foreach (array('csrf_expire', 'csrf_token_name', 'csrf_cookie_name') as $key)
{
if (FALSE !== ($val = config_item($key)))
{
$this->{'_'.$key} = $val;
}
}
if (config_item('cookie_prefix'))
{
$this->_csrf_cookie_name = config_item('cookie_prefix').$this->_csrf_cookie_name;
}
// 为csrf生成hash串
$this->_csrf_set_hash();
}
log_message('debug', "Security Class Initialized");
}
// 验证csrf
public function csrf_verify()
{
if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST')
{ //请求方式非POST 设置csrf csrf 是对POST请求进行的验证
return $this->csrf_set_cookie();
}
if ( ! isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]))
{
$this->csrf_show_error(); // form表单的csrf 跟cookie里面的csrf都为空
}
if ($_POST[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name])
{
$this->csrf_show_error(); //两个csrf的值不相等
}
//去除csrf
unset($_POST[$this->_csrf_token_name]);
unset($_COOKIE[$this->_csrf_cookie_name]);
// 重新生成csrf hash 并发送cookie
$this->_csrf_set_hash();
$this->csrf_set_cookie();
log_message('debug', 'CSRF token verified');
return $this;
}
// csrf添加到cookie
public function csrf_set_cookie()
{
$expire = time() + $this->_csrf_expire;//保存时间
$secure_cookie = (config_item('cookie_secure') === TRUE) ? 1 : 0;
if ($secure_cookie && (empty($_SERVER['HTTPS']) OR strtolower($_SERVER['HTTPS']) === 'off'))
{
return FALSE; //是否经过 https
}
setcookie($this->_csrf_cookie_name, $this->_csrf_hash, $expire, config_item('cookie_path'), config_item('cookie_domain'), $secure_cookie);
log_message('debug', "CRSF cookie Set");
return $this;
}
public function csrf_show_error()
{
show_error('The action you have requested is not allowed.');
}
public function get_csrf_hash()
{
return $this->_csrf_hash;
}
public function get_csrf_token_name()
{
return $this->_csrf_token_name;
}
// --------------------------------------------------------------------
/**
* XSS Clean
*
* Sanitizes data so that Cross Site Scripting Hacks can be
* prevented. This function does a fair amount of work but
* it is extremely thorough, designed to prevent even the
* most obscure XSS attempts. Nothing is ever 100% foolproof,
* of course, but I haven't been able to get anything passed
* the filter.
*
* Note: This function should only be used to deal with data
* upon submission. It's not something that should
* be used for general runtime processing.
*
* This function was based in part on some code and ideas I
* got from Bitflux: http://channel.bitflux.ch/wiki/XSS_Prevention
*
* To help develop this script I used this great list of
* vulnerabilities along with a few other hacks I've
* harvested from examining vulnerabilities in other programs:
* http://ha.ckers.org/xss.html
*
* @param mixed string or array
* @param bool
* @return string
*/
public function xss_clean($str, $is_image = FALSE)
{
if (is_array($str))
{
while (list($key) = each($str))
{
$str[$key] = $this->xss_clean($str[$key]);
}
return $str;
}
// 去除无法显示的字符
$str = remove_invisible_characters($str);
// 过滤实体
$str = $this->_validate_entities($str);
$str = rawurldecode($str);//对URL进行解码
// 过滤HTML标签属性特别是属性值 匹配到 attr='val' or attr="val" 的形式
$str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", array($this, '_convert_attribute'), $str);
//解码 实体
// ?= 零宽先行断言 匹配后面表达式前面的位置 表达式开始位置
$str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", array($this, '_decode_entity'), $str);
$str = remove_invisible_characters($str);
if (strpos($str, "\t") !== FALSE)
{
$str = str_replace("\t", ' ', $str);//空格代替 \t
}
$converted_string = $str;
// 替换掉关键字
$str = $this->_do_never_allowed($str);
if ($is_image === TRUE)
{
// 转义php脚本格式的数据 对 <?php 中的 '<' 转义成 <
$str = preg_replace('/<\?(php)/i', "<?\\1", $str);
}
else
{ //转义XML格式的数据格式
$str = str_replace(array('<?', '?'.'>'), array('<?', '?>'), $str);
}
$words = array(
'javascript', 'expression', 'vbscript', 'script', 'base64',
'applet', 'alert', 'document', 'write', 'cookie', 'window'
);
foreach ($words as $word)
{
$temp = '';
for ($i = 0, $wordlen = strlen($word); $i < $wordlen; $i++)
{
// 通过words形成 j\s*a\s*v\s*a\s*s\s*c\s*r\s*i\s*p\s*t\s*
$temp .= substr($word, $i, 1)."\s*";
}
// 先 substr($temp,0,-3) 去掉 words中最后三个字符 '\s*'
// 匹配到任意中间空格的关键字 然后callback函数去除关键字中间的空格
// 防止用关键字中间空格 伪造出脚本
$str = preg_replace_callback('#('.substr($temp, 0, -3).')(\W)#is', array($this, '_compact_exploded_words'), $str);
}
do
{
$original = $str;
if (preg_match("/<a/i", $str))
{
// 匹配到a标签
$str = preg_replace_callback("#<a\s+([^>]*?)(>|$)#si", array($this, '_js_link_removal'), $str);
}
if (preg_match("/<img/i", $str))
{
// 匹配到img标签
$str = preg_replace_callback("#<img\s+([^>]*?)(\s?/?>|$)#si", array($this, '_js_img_removal'), $str);
}
if (preg_match("/script/i", $str) OR preg_match("/xss/i", $str))
{
// 匹配到脚本script标签
$str = preg_replace("#<(/*)(script|xss)(.*?)\>#si", '[removed]', $str);
}
}
while($original != $str);//过滤不干净就继续过滤
unset($original);
//移除事件属性
$str = $this->_remove_evil_attributes($str, $is_image);
$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';
// 1 2 3 4
$str = preg_replace_callback('#<(/*\s*)('.$naughty.')([^><]*)([><]*)#is', array($this, '_sanitize_naughty_html'), $str);
// 过滤函数调用 eval()、alert()、cmd()、... 将 ( ) 转义成 HTML 十进制代码
$str = preg_replace('#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si', "\\1\\2(\\3)", $str);
// Final clean up
$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) ? TRUE: FALSE;
}
log_message('debug', "XSS Filtering completed");
return $str;
}
public function xss_hash()
{
// 生成hash
if ($this->_xss_hash == '')
{
mt_srand();
$this->_xss_hash = md5(time() + mt_rand(0, 1999999999));
}
return $this->_xss_hash;
}
// html_entity_decode 将html实体转换成字符串 但是它不能对HTML十进制形式转换
public function entity_decode($str, $charset='UTF-8')
{
if (stristr($str, '&') === FALSE)
{
return $str;//不需要解码
}
// 下面解决不能转换的问题
$str = html_entity_decode($str, ENT_COMPAT, $charset);
// hexdec 将十六进制转换为十进制
// 将HTML实体编码 &#XX 中 XX 部分的十六进制转换为十进制
$str = preg_replace('~&#x(0*[0-9a-f]{2,5})~ei', 'chr(hexdec("\\1"))', $str);
//&#xx HTML实体 XX 转换为对应的字符
return preg_replace('~&#([0-9]{2,4})~e', 'chr(\\1)', $str);
}
/*
去除文件名中不合法的字符 并且对一些字符转义
*/
public function sanitize_filename($str, $relative_path = FALSE)
{
$bad = array(
"../",
"<!--",
"-->",
"<",
">",
"'",
'"',
'&',
'$',
'#',
'{',
'}',
'[',
']',
'=',
';',
'?',
"%20",
"%22",
"%3c", // <
"%253c", // <
"%3e", // >
"%0e", // >
"%28", // (
"%29", // )
"%2528", // (
"%26", // &
"%24", // $
"%3f", // ?
"%3b", // ;
"%3d" // =
);
if ( ! $relative_path)
{
$bad[] = './';
$bad[] = '/';
}
$str = remove_invisible_characters($str, FALSE);
// 去除文件名中禁止出现的字符 并且删除转义字符
return stripslashes(str_replace($bad, '', $str));
}
protected function _compact_exploded_words($matches)
{//剔除1中的空格
return preg_replace('/\s+/s', '', $matches[1]).$matches[2];
}
protected function _remove_evil_attributes($str, $is_image)
{
// 所有有on开头的属性
$evil_attributes = array('on\w*', 'style', 'xmlns', 'formaction');
if ($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 attribute strings with quotes (042 and 047 are octal quotes 八进制引号)
// 匹配带引号的属性 042 047 八进制引号 e.g. attr='value'
preg_match_all('/('.implode('|', $evil_attributes).')\s*=\s*(\042|\047)([^\\2]*?)(\\2)/is', $str, $matches, PREG_SET_ORDER);
foreach ($matches as $attr)
{
// 对匹配到的内容进行转义
$attribs[] = preg_quote($attr[0], '/');
}
// find attribute strings without quotes
// 匹配 不 带引号的属性 e.g. attr=value
preg_match_all('/('.implode('|', $evil_attributes).')\s*=\s*([^\s>]*)/is', $str, $matches, PREG_SET_ORDER);
foreach ($matches as $attr)
{
$attribs[] = preg_quote($attr[0], '/');
}
// 去除字符串中HTML标签里面的 这种 onclick = 'javascript:func();'
if (count($attribs) > 0)
{
// 1 2 3 4 5 6 7 8
$str = preg_replace('/(<?)(\/?[^><]+?)([^A-Za-z<>\-])(.*?)('.implode('|', $attribs).')(.*?)([\s><]?)([><]*)/i', '$1$2 $4$6$7$8', $str, -1, $count);
}
} while ($count);
return $str;
}
protected function _sanitize_naughty_html($matches)
{
// encode opening brace
$str = '<'.$matches[1].$matches[2].$matches[3];
// encode captured opening or closing brace to prevent recursive vectors
$str .= str_replace(array('>', '<'), array('>', '<'),$matches[4]);
return $str;
}
protected function _js_link_removal($match)
{
return str_replace(
$match[1], // match[1]里面是属性
preg_replace(// 如果a标签的href值是危险的内容 将href带值一起干掉
'#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|data\s*:)#si',
'',
$this->_filter_attributes(str_replace(array('<', '>'), '', $match[1]))
),
$match[0]
);
}
protected function _js_img_removal($match)
{
return str_replace(
$match[1],
preg_replace(//去除 img 标签属性
'#src=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si',
'',
$this->_filter_attributes(str_replace(array('<', '>'), '', $match[1]))
),
$match[0]
);
}
/*
将字符串中的 > < \ 三个字符转换成HTML实体
防范<a href='<?php phpcode ...;?>'> 这样嵌入php代码的xss攻击形式
*/
protected function _convert_attribute($match)
{
return str_replace(array('>', '<', '\\'), array('>', '<', '\\\\'), $match[0]);
}
protected function _filter_attributes($str)
{
$out = '';
// 匹配 attr = 'val' or attr = "val"
if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches))
{
foreach ($matches[0] as $match)
{
// 去除 里面的注释 /*some*/
$out .= preg_replace("#/\*.*?\*/#s", '', $match);
}
}
return $out;
}
protected function _decode_entity($match)
{
return $this->entity_decode($match[0], strtoupper(config_item('charset')));
}
// 过滤URL实体
/*
get方式传递HTML十进制编码 &#XX;
& # ; 这些是url中的保留关键字 传递不过去的
我们可以对其进行uriencode --> %26%23XX%3b
*/
protected function _validate_entities($str)
{
// &var=val --> xss_hash+var=val 起到保护作用
$str = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-]+)|i', $this->xss_hash()."\\1=\\2", $str);
// 十进制HTML实体表示
// \x00-\x20 --> ASCII 0-32 不能直接显示的字符 如果有不能显示的字符将他移动到 ';' 后面
$str = preg_replace('#(&\#?[0-9a-z]{2,})([\x00-\x20])*;?#i', "\\1;\\2", $str);
/*
* Validate UTF16 two byte encoding (x00)
*/
$str = preg_replace('#(&\#x?)([0-9A-F]+);?#i',"\\1\\2;",$str);
// 又把xss_hash 替换成了& 实现保护作用 因为中间的处理有 & 符号
$str = str_replace($this->xss_hash(), '&', $str);
return $str;
}
// 替换字符串中绝对不允许出现的字符串组合
// 防止与HTML实体组合构造出标签进行xss攻击
protected function _do_never_allowed($str)
{//val replace the key
$str = str_replace(array_keys($this->_never_allowed_str), $this->_never_allowed_str, $str);
foreach ($this->_never_allowed_regex as $regex)
{//match and replaced by [removed]
$str = preg_replace('#'.$regex.'#is', '[removed]', $str);
}
return $str;
}
protected function _csrf_set_hash()
{
if ($this->_csrf_hash == '')
{
//csrf 已经存在在cookie里面 对属性_csrf_hash进行一次赋值返回
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];
}
// 生成
return $this->_csrf_hash = md5(uniqid(rand(), TRUE));
}
return $this->_csrf_hash;
}
}
Code Tips：
主要是正则的写法 以及各种xss的攻击形式以防范策略
这个安全类是CI中（DB还没看）最大的一个类了把
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