Web信息安全实践_3.4 CSRF防御

Referer: http://www.myzoo.com/transfer.php

Referer: http://www.attacker.com/csrf/csrf1.html

<script>
    if(document.referrer.indexOf(‘bank.com‘)<0)
    document.location.replace("https://www.ustc.edu.cn");
</script>

$ref = ($_SERVER[‘HTTP_REFERER‘]);    
$tmp2 = substr($tmp1,0,strpos($tmp1,‘/‘));
if($tmp2 !=‘www.bank.com‘)
    die("Hotlinking not permitted!");
else
    echo($refData[‘host‘])

sudo vim /var/www/myzoo/login.php
// 在头部处添加如下四行
<?php
session_start(); //启动session
if($_POST[‘login_username‘]!=NULL && $_POST[‘login_password‘]!=NULL)
 $_SESSION[‘csrf‘] = md5(uniqid(mt_rand(),true)); //在session中产生一个随机数，并且通过MD5k进行散列
?>
//构造随机数，每次用户登录生成一个随机数.
//开发者控制粒度，譬如，用户登录页面，用户登录期间使用一个随机数，用户转账页面，每次转账更新一次数据......

sudo vim /var/www/myzoo/transfer.php
<!--将session中生成的值放在表单-->
<form method=POST name=transferform action="<?php echo $_SERVER[‘PHP_SELF‘]?>">
<p><input name=csrf type=hidden value="<?php echo $_SESSION[‘csrf‘]?>"></p> <!--将session中生成的值放在表单-->
<p>Send <input name=zoobars type=text value="<?php echo $_POST[‘zoobars‘];?>" size=5> zoobars</p>
<p>to <input name=recipient type=text value="<?php echo $_POST[‘recipient‘];?>"></p>
<input type=submit name=submission value="Send">
</form>

//检测如果csrf字段不正确就停止操作
sudo vim /var/www/myzoo/transfer.php
if($_POST[‘submission‘]) {

//    if(1){
    if($_POST[‘csrf‘] == $_SESSION[‘csrf‘]) {//用户提交token值和生成的token值是否一样
    $recipient = $_POST[‘recipient‘];
    $zoobars = (int) $_POST[‘zoobars‘];
    $sql = "SELECT Zoobars FROM Person WHERE PersonID=$user->id";
    $rs = $db->executeQuery($sql);
    $rs = mysql_fetch_array($rs);
    $sender_balance = $rs["Zoobars"] - $zoobars;
    $sql = "SELECT PersonID FROM Person WHERE Username=‘$recipient‘";
    $rs = $db->executeQuery($sql);
    $rs = mysql_fetch_array($rs);
    $recipient_exists = $rs["PersonID"];
    if($zoobars > 0 && $sender_balance >= 0 && $recipient_exists) {
      $sql = "UPDATE Person SET Zoobars = $sender_balance " .
             "WHERE PersonID=$user->id";
      $db->executeQuery($sql);
      $sql = "SELECT Zoobars FROM Person WHERE Username=‘$recipient‘";
      $rs = $db->executeQuery($sql);
        $rs = mysql_fetch_array($rs);
      $recipient_balance = $rs["Zoobars"] + $zoobars;
      $sql = "UPDATE Person SET Zoobars = $recipient_balance " .
             "WHERE Username=‘$recipient‘";
      $db->executeQuery($sql);
      $result = "Sent $zoobars zoobars";
    }
    else $result = "Transfer to $recipient failed.";
   }
   else return;//如果csrf字段不正确,停止操作
  }
?>