XSS防护措施浅析（反射型/存储型）1. 编码策略尽量Review。。不要把危险的位置直接留给输入参数。 2. 特别针

一些例子

有单引号

<body onload=alert('test1')>

无单引号

<img src="http://url.to.file.which/not.exist" onerror=alert(document.cookie);>

借助Encoded URI Schemes

<IMG SRC=j&#X41vascript:alert('test2')>

利用编码算法

<META HTTP-EQUIV="refresh"
CONTENT="0;url=data:text/html;base64,PHNjcmlwdD5hbGVydCgndGVzdDMnKTwvc2NyaXB0Pg">

防护措施（反射型/存储型）

1. 编码策略

尽量Review。。不要把危险的位置直接留给输入参数。

2. 特别针对反射型

设置HTTP-ONLY缓解 XSS 攻击
检验请求的Referer参数
响应头加入Content-Security-Policy，限制资源文件的加载源头

3. 过滤类型

如果要求输入的是number, 就严格校验输入的参数类型为number，这样直接避免这些参数发生XSS。

4. 验证有效性

通常，我们可以给参数的长度，预估一个有效长度、具有某些特定格式（例如@emal.com）、以及其他的合法业务意义（例如该id代表的数据是否存在），这样也可以避免一部分xss的攻击。

5. 清洗参数

这一步最好在「验证有效性」之前执行

5.1 常见的PHP过滤函数

// 1. 清理空格
$str = trim($_POST['name']);
// 2. 过滤html标签
$str = strip_tags($str);
// 3. 将特定字符内容转化为html实体, ENT_QUOTES表示编码双引号和单引号
$str = htmlspecialchars($str, ENT_QUOTES);
// 4. 某些攻击代码不含单引号：alert(1) 、alert(document.cookie)
$str = json_encode(htmlspecialchars($str));

5.2 白名单黑名单机制

禁止所有富文本内事件，
设立黑名单标签/属性，例如：<iframe>，<script>，<base>，<form>
设立白名单标签/属性，认为安全的内容才能嵌入，例如：<a>，<img>，<div>

5.3 考虑特殊字符（代码来自搜索引擎）

my.oschina.net/sharesuiyue…

//Remove the exploer'bug XSS
function RemoveXSS($val) {
   // remove all non-printable characters. CR(0a) and LF(0b) and TAB(9) are allowed
   // this prevents some character re-spacing such as <java\0script>
   // note that you have to handle splits with \n, \r, and \t later since they *are* allowed in some inputs
   $val = preg_replace('/([\x00-\x08,\x0b-\x0c,\x0e-\x19])/', '', $val);
   // straight replacements, the user should never need these since they're normal characters
   // this prevents like <IMG SRC=@avascript:alert('XSS')>
   $search = 'abcdefghijklmnopqrstuvwxyz';
   $search .= 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
   $search .= '1234567890!@#$%^&*()';
   $search .= '~`";:?+/={}[]-_|\'\\';
   for ($i = 0; $i < strlen($search); $i++) {
      // ;? matches the ;, which is optional
      // 0{0,7} matches any padded zeros, which are optional and go up to 8 chars
      // @ @ search for the hex values
      $val = preg_replace('/(&#[xX]0{0,8}'.dechex(ord($search[$i])).';?)/i', $search[$i], $val); // with a ;
      // @ @ 0{0,7} matches '0' zero to seven times
      $val = preg_replace('/(&#0{0,8}'.ord($search[$i]).';?)/', $search[$i], $val); // with a ;
   }
   // now the only remaining whitespace attacks are \t, \n, and \r
   $ra1 = array('javascript', 'vbscript', 'expression', 'applet', 'meta', 'xml', 'blink', 'link', 'style', 'script', 'embed', 'object', 'iframe', 'frame', 'frameset', 'ilayer', 'layer', 'bgsound', 'title', 'base');
   $ra2 = array('onabort', 'onactivate', 'onafterprint', 'onafterupdate', 'onbeforeactivate', 'onbeforecopy', 'onbeforecut', 'onbeforedeactivate', 'onbeforeeditfocus', 'onbeforepaste', 'onbeforeprint', 'onbeforeunload', 'onbeforeupdate', 'onblur', 'onbounce', 'oncellchange', 'onchange', 'onclick', 'oncontextmenu', 'oncontrolselect', 'oncopy', 'oncut', 'ondataavailable', 'ondatasetchanged', 'ondatasetcomplete', 'ondblclick', 'ondeactivate', 'ondrag', 'ondragend', 'ondragenter', 'ondragleave', 'ondragover', 'ondragstart', 'ondrop', 'onerror', 'onerrorupdate', 'onfilterchange', 'onfinish', 'onfocus', 'onfocusin', 'onfocusout', 'onhelp', 'onkeydown', 'onkeypress', 'onkeyup', 'onlayoutcomplete', 'onload', 'onlosecapture', 'onmousedown', 'onmouseenter', 'onmouseleave', 'onmousemove', 'onmouseout', 'onmouseover', 'onmouseup', 'onmousewheel', 'onmove', 'onmoveend', 'onmovestart', 'onpaste', 'onpropertychange', 'onreadystatechange', 'onreset', 'onresize', 'onresizeend', 'onresizestart', 'onrowenter', 'onrowexit', 'onrowsdelete', 'onrowsinserted', 'onscroll', 'onselect', 'onselectionchange', 'onselectstart', 'onstart', 'onstop', 'onsubmit', 'onunload');
   $ra = array_merge($ra1, $ra2);
   $found = true; // keep replacing as long as the previous round replaced something
   while ($found == true) {
      $val_before = $val;
      for ($i = 0; $i < sizeof($ra); $i++) {
         $pattern = '/';
         for ($j = 0; $j < strlen($ra[$i]); $j++) {
            if ($j > 0) {
               $pattern .= '(';
               $pattern .= '(&#[xX]0{0,8}([9ab]);)';
               $pattern .= '|';
               $pattern .= '|(&#0{0,8}([9|10|13]);)';
               $pattern .= ')*';
            }
            $pattern .= $ra[$i][$j];
         }
         $pattern .= '/i';
         $replacement = substr($ra[$i], 0, 2).'<x>'.substr($ra[$i], 2); // add in <> to nerf the tag
         $val = preg_replace($pattern, $replacement, $val); // filter out the hex tags
         if ($val_before == $val) {
            // no replacements were made, so exit the loop
            $found = false;
         }
      }
   }
   return $val;
}