CI安全类提供了全局防御CSRF攻击和XSS攻击策略，只需要在配置文件开启即可：

复制代码 代码如下:
$config['csrf_protection'] = TRUE;
$config['global_xss_filtering'] = TRUE;

并提供了实用方法：

复制代码 代码如下:
$this->security->xss_clean($data);//第二个参数为TRUE，验证图片安全
$this->security->sanitize_filename()//过滤文件名

CI也提供了安全函数：

xss_clean()//xss过滤
sanitize_filename()//净化文件名
do_hash()//md5或sha加密
strip_image_tags() //删除图片标签的不必要字符
encode_php_tags()//把PHP脚本标签强制转成实体对象

复制代码 代码如下:
<"([\"'])"
 );
 //构造函数
 public function __construct()
 {
  // CSRF保护是否开启
  if (config_item('csrf_protection') === TRUE)
  {
   // CSRF配置
   foreach (array('csrf_expire', 'csrf_token_name', 'csrf_cookie_name') as $key)
   {
    if (FALSE !== ($val = config_item($key)))
    {
     $this->{'_'.$key} = $val;
    }
   }
   // _csrf_cookie_name加上cookie前缀
   if (config_item('cookie_prefix'))
   {
    $this->_csrf_cookie_name = config_item('cookie_prefix').$this->_csrf_cookie_name;
   }
   // 设置csrf的hash值
   $this->_csrf_set_hash();
  }
  log_message('debug', "Security Class Initialized");
 }
 // --------------------------------------------------------------------
 /**
  * Verify Cross Site Request Forgery Protection
  *
  * @return object
  */
 public function csrf_verify()
 {
  // 如果不是post请求，则设置csrf的cookie值
  if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST')
  {
   return $this->csrf_set_cookie();
  }
  // Do the tokens exist in both the _POST and _COOKIE arrays"CRSF cookie Set");
  return $this;
 }
 //csrf保存
 public function csrf_show_error()
 {
  show_error('The action you have requested is not allowed.');
 }
 //获取csrf的hash值
 public function get_csrf_hash()
 {
  return $this->_csrf_hash;
 }
 //获取csrf的token值
 public function get_csrf_token_name()
 {
  return $this->_csrf_token_name;
 }
 /**
  * XSS 过滤
  */
 public function xss_clean($str, $is_image = FALSE)
 {
  //是否是数组
  if (is_array($str))
  {
   while (list($key) = each($str))
   {
    $str[$key] = $this->xss_clean($str[$key]);
   }
   return $str;
  }
  //去掉可见字符串
  $str = remove_invisible_characters($str);
  // 验证实体url
  $str = $this->_validate_entities($str);
  /*
   * URL 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
   *
   */
  $str = rawurldecode($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.
   *
   */
  $str = preg_replace_callback("/[a-z]+=([\'\"]).*", array($this, '_convert_attribute'), $str);
  $str = preg_replace_callback("/<\w+.*", array($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:
   *
   * <"<", $str);
  }
  else
  {
   $str = str_replace(array('<"\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
   * We used to do some version comparisons and use of stripos for PHP5,
   * but it is dog slow compared to these simplified non-capturing
   * preg_match(), especially if the pattern exists in the string
   */
  do
  {
   $original = $str;
   if (preg_match("/<a/i", $str))
   {
    $str = preg_replace_callback("#<a\s+([^>]*", array($this, '_js_link_removal'), $str);
   }
   if (preg_match("/<img/i", $str))
   {
    $str = preg_replace_callback("#<img\s+([^>]*", array($this, '_js_img_removal'), $str);
   }
   if (preg_match("/script/i", $str) OR preg_match("/xss/i", $str))
   {
    $str = preg_replace("#<(/*)(script|xss)(.*", '[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>
   * Becomes: <blink>
   */
  $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.
   *
   * For example: eval('some code')
   * Becomes:  eval('some code')
   */
  $str = preg_replace('#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*"\\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) "XSS Filtering completed");
  return $str;
 }
 // --------------------------------------------------------------------
 //保护url的随机hash值
 public function xss_hash()
 {
  if ($this->_xss_hash == '')
  {
   mt_srand();
   $this->_xss_hash = md5(time() + mt_rand(0, 1999999999));
  }
  return $this->_xss_hash;
 }
 // --------------------------------------------------------------------
 /**
  * html实体转码
  */
 public function entity_decode($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)', $str);
 }
 // --------------------------------------------------------------------
 //过滤文件名，保证文件名安全
 public function sanitize_filename($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);
  return stripslashes(str_replace($bad, '', $str));
 }
 //压缩单词如j a v a s c r i p t成javascript
 protected function _compact_exploded_words($matches)
 {
  return preg_replace('/\s+/s', '', $matches[1]).$matches[2];
 }
 // --------------------------------------------------------------------
 /*
  * 去掉一些危害的html属性
  */
 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 strings with quotes (042 and 047 are octal quotes)
   preg_match_all('/('.implode('|', $evil_attributes).')\s*=\s*(\042|\047)([^\\2]*"file://\\2)/is'">\\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('/(<"#/\*.*", '', $match);
   }
  }
  return $out;
 }
 // --------------------------------------------------------------------
 //html实体转码
 protected function _decode_entity($match)
 {
  return $this->entity_decode($match[0], strtoupper(config_item('charset')));
 }
 // --------------------------------------------------------------------
 /**
  * 验证url实体
  */
 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('#(&\#"\\1;\\2", $str);
  /*
   * Validate UTF16 two byte encoding (x00)
   *
   * Just as above, adds a semicolon if missing.
   *
   */
  $str = preg_replace('#(&\#x"\\1\\2;",$str);
  /*
   * Un-Protect GET variables in URLs
   */
  $str = str_replace($this->xss_hash(), '&', $str);
  return $str;
 }
 // ----------------------------------------------------------------------
 //过滤不允许出现的字符串
 protected function _do_never_allowed($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 $str;
 }
 // --------------------------------------------------------------------
 //设置csrf的hash值
 protected function _csrf_set_hash()
 {
  if ($this->_csrf_hash == '')
  {
   // 如果_csrf_cookie_name存在，直接作为csrf hash值
   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];
   }
                        //否则随机一个md5字符串
   return $this->_csrf_hash = md5(uniqid(rand(), TRUE));
  }
  return $this->_csrf_hash;
 }
}