php防止伪造跨站请求实现程序

CSRF站外类型的漏洞其实就是传统意义上的外部提交数据问题，一般程序员会考虑给一些留言评论等的表单加上水印以防止SPAM问题，但是为了用户的体验性，一些操作可能没有做任何限制，所以攻击者可以先预测好请求的参数，在站外的Web页面里编写javascript脚本伪造文件请求或和自动提交的表单来实现GET、POST请求，用户在会话状态下点击链接访问站外的Web页面，客户端就被强迫发起请求。

浏览器的安全缺陷

现在的Web应用程序几乎都是使用Cookie来识别用户身份以及保存会话状态，但是所有的浏览器在最初加入Cookie功能时并没有考虑安全因素，从 WEB页面产生的文件请求都会带上COOKIE，如下图所示，Web页面中的一个正常的图片所产生的请求也会带上COOKIE：

GET http://website.com/log.jpg

Cookie: session_id

客户端 ——————————————————-服务器

咱们按照这个思路，山寨一个crumb的实现，代码如下：

 

代码如下

复制代码

class Crumb {                                                                                                                                                                                                               CONST SALT = "your-secret-salt";                                                                                                                              static $ttl = 7200;                                                                                                                                                                                                     static public function challenge($data) {                                                                             return hash_hmac('md5', $data, self::SALT);                                                                   }                                                                                                                                                                                                                                   static public function issueCrumb($uid, $action = -1) {                                                               $i = ceil(time() / self::$ttl);                                                                                   return substr(self::challenge($i . $action . $uid), -12, 10);                                                 }                                                                                                                                                                                                                                   static public function verifyCrumb($uid, $crumb, $action = -1) {                                                      $i = ceil(time() / self::$ttl);                                                                                                                                                                                                     if(substr(self::challenge($i . $action . $uid), -12, 10) == $crumb ||                                                 substr(self::challenge(($i - 1) . $action . $uid), -12, 10) == $crumb)                                            return true;                                                                                                                                                                                                                    return false;                                                                                                 }                                                                                                                                                                                                                               }

代码中的$uid表示用户唯一标识，而$ttl表示这个随机串的有效时间。

应用示例

在表单中插入一个隐藏的随机串crumb

代码如下	复制代码

处理表单 demo.php
对crumb进行检查

代码如下	复制代码
if(Crumb::verifyCrumb($uid, $_POST['crumb'])) {     //按照正常流程处理表单 } else {     //crumb校验失败，错误提示流程 }

注意:

CSRF攻击和相关web蠕虫的爆发,并且针对这类web攻击制定有效的应急措施。同建议程序员不要滥用$_REQUEST类变量，在必要的情况下给某些敏感的操作加上水印，考虑使用类似DISCUZ论坛的formhash技术提高黑客预测请求参数的难度，注意JSON数据接口的安全问题等