CSRF漏洞（原理、DVWA实验、修复建议）

古城微笑少年丶 2022-12-08 15:48 512阅读 0赞

**目录**

1 介绍CSRF漏洞

2 CSRF漏洞的原理

3 DVWA CSRF实验过程

3.1 low级别

3.2 medium级别

相关函数说明

3.3 high级别

3.4 impossible级别

4 CSRF漏洞修复建议

--------------------

# 1 介绍CSRF漏洞 #

CSRF (Cross -site request forgery，跨站请求伪造)也被称为One Click Attack或者Session Riding，通常缩写为CSRF或者XSRF，是一种对网站的恶意利用。尽管听起来像跨站脚本(XSS)，但它与XSS非常不同，XSS利用站点内的信任用户，而CSRF则通过伪装成受信任用户请求受信任的网站。与XSS攻击相比，CSRF攻击往往不大流行(因此对其进行防范的资源也相当稀少)也难以防范，所以被认为比XSS更具  
危险性。CSRF漏洞经常被用来制作蠕虫攻击、刷SEO流量等。

# 2 CSRF漏洞的原理 #

其实可以这样理解CSRF：攻击者利用目标用户的身份，以目标用户的名义执行某些非法操作。CSRF能够做的事情包括:以目标用户的名义发送邮件、发消息，盗取目标用户的账号，甚至购买商品、虚拟货币转账，这会泄露个人隐私并威胁到了目标用户的财产安全。  
举个例子，你想给某位用户转账100元，那么单击"转账” 按钮后，发出的HTTP请求会与http://www.xxbank.com/pay.php?user=xx&money=100类似。而攻击者构造链接(http://www.xxbank.com/pay.php?user=hack&money=100)，当目标用户访问了该URL后，就会自动向Hack账号转账100元，而且这只涉及目标用户的操作，攻击者并没有获取目标用户的cookie或其他信息。  
CSRF的攻击过程有以下两个重点。

*  目标用户已经登录了网站，能够执行网站的功能。
 *  目标用户访问了攻击者构造的URL。

# 3 DVWA CSRF实验过程 #

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70][]

## 3.1 low级别 ##

<?php
    
    if( isset( $_GET[ 'Change' ] ) ) {
        // Get input
        $pass_new  = $_GET[ 'password_new' ];
        $pass_conf = $_GET[ 'password_conf' ];
    
        // Do the passwords match?
        if( $pass_new == $pass_conf ) {
            // They do!
            $pass_new = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass_new ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
            $pass_new = md5( $pass_new );
    
            // Update the database
            $insert = "UPDATE `users` SET password = '$pass_new' WHERE user = '" . dvwaCurrentUser() . "';";
            $result = mysqli_query($GLOBALS["___mysqli_ston"],  $insert ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );
    
            // Feedback for the user
            echo "<pre>Password Changed.</pre>";
        }
        else {
            // Issue with passwords matching
            echo "<pre>Passwords did not match.</pre>";
        }
    
        ((is_null($___mysqli_res = mysqli_close($GLOBALS["___mysqli_ston"]))) ? false : $___mysqli_res);
    }
    
    ?>

可以看到，服务器收到修改密码的请求后，会检查参数password\_new与password\_conf是否相同，如果相同，就会修改密码，并没有任何的防CSRF机制（当然服务器对请求的发送者是做了身份验证的，是检查的cookie，只是这里的代码没有体现）。

于是直接构造链接访问即可。[http://192.168.1.100/dvwa/vulnerabilities/csrf/?password\_new=password&password\_conf=password&Change=Change\#][http_192.168.1.100_dvwa_vulnerabilities_csrf_password_new_password_password_conf_password_Change_Change]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 1][]

## 3.2 medium级别 ##

<?php
    
    if( isset( $_GET[ 'Change' ] ) ) {
        // Checks to see where the request came from
        if( stripos( $_SERVER[ 'HTTP_REFERER' ] ,$_SERVER[ 'SERVER_NAME' ]) !== false ) {
            // Get input
            $pass_new  = $_GET[ 'password_new' ];
            $pass_conf = $_GET[ 'password_conf' ];
    
            // Do the passwords match?
            if( $pass_new == $pass_conf ) {
                // They do!
                $pass_new = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass_new ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
                $pass_new = md5( $pass_new );
    
                // Update the database
                $insert = "UPDATE `users` SET password = '$pass_new' WHERE user = '" . dvwaCurrentUser() . "';";
                $result = mysqli_query($GLOBALS["___mysqli_ston"],  $insert ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );
    
                // Feedback for the user
                echo "<pre>Password Changed.</pre>";
            }
            else {
                // Issue with passwords matching
                echo "<pre>Passwords did not match.</pre>";
            }
        }
        else {
            // Didn't come from a trusted source
            echo "<pre>That request didn't look correct.</pre>";
        }
    
        ((is_null($___mysqli_res = mysqli_close($GLOBALS["___mysqli_ston"]))) ? false : $___mysqli_res);
    }
    
    ?>

### **相关函数说明** ###

int eregi(string pattern, string string)  
检查string中是否含有pattern（不区分大小写），如果有返回True，反之False。  
可以看到，Medium级别的代码检查了保留变量 HTTP\_REFERER（http包头的Referer参数的值，表示来源地址）中是否包含SERVER\_NAME（http包头的Host参数，及要访问的主机名，这里是192.168.1.100），希望通过这种机制抵御CSRF攻击。

referer头信息可以用burp suite的截断功能修改  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 2][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 3][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 4][]

## 3.3 high级别 ##

<?php
    
    if( isset( $_GET[ 'Change' ] ) ) {
        // Check Anti-CSRF token
        checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );
    
        // Get input
        $pass_new  = $_GET[ 'password_new' ];
        $pass_conf = $_GET[ 'password_conf' ];
    
        // Do the passwords match?
        if( $pass_new == $pass_conf ) {
            // They do!
            $pass_new = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass_new ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
            $pass_new = md5( $pass_new );
    
            // Update the database
            $insert = "UPDATE `users` SET password = '$pass_new' WHERE user = '" . dvwaCurrentUser() . "';";
            $result = mysqli_query($GLOBALS["___mysqli_ston"],  $insert ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );
    
            // Feedback for the user
            echo "<pre>Password Changed.</pre>";
        }
        else {
            // Issue with passwords matching
            echo "<pre>Passwords did not match.</pre>";
        }
    
        ((is_null($___mysqli_res = mysqli_close($GLOBALS["___mysqli_ston"]))) ? false : $___mysqli_res);
    }
    
    // Generate Anti-CSRF token
    generateSessionToken();
    
    ?>

可以看到，High级别的代码加入了Anti-CSRF token机制，用户每次访问改密页面时，服务器会返回一个随机的token，向服务器发起请求时，需要提交token参数，而服务器在收到请求时，会优先检查token，只有token正确，才会处理客户端的请求。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 5][]  
后续：[https://www.jianshu.com/p/4eed0faaf0ca][https_www.jianshu.com_p_4eed0faaf0ca]

或者：[https://www.freebuf.com/articles/web/118352.html][https_www.freebuf.com_articles_web_118352.html]

## 3.4 impossible级别 ##

<?php
    
    if( isset( $_GET[ 'Change' ] ) ) {
        // Check Anti-CSRF token
        checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );
    
        // Get input
        $pass_curr = $_GET[ 'password_current' ];
        $pass_new  = $_GET[ 'password_new' ];
        $pass_conf = $_GET[ 'password_conf' ];
    
        // Sanitise current password input
        $pass_curr = stripslashes( $pass_curr );
        $pass_curr = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass_curr ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
        $pass_curr = md5( $pass_curr );
    
        // Check that the current password is correct
        $data = $db->prepare( 'SELECT password FROM users WHERE user = (:user) AND password = (:password) LIMIT 1;' );
        $data->bindParam( ':user', dvwaCurrentUser(), PDO::PARAM_STR );
        $data->bindParam( ':password', $pass_curr, PDO::PARAM_STR );
        $data->execute();
    
        // Do both new passwords match and does the current password match the user?
        if( ( $pass_new == $pass_conf ) && ( $data->rowCount() == 1 ) ) {
            // It does!
            $pass_new = stripslashes( $pass_new );
            $pass_new = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass_new ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
            $pass_new = md5( $pass_new );
    
            // Update database with new password
            $data = $db->prepare( 'UPDATE users SET password = (:password) WHERE user = (:user);' );
            $data->bindParam( ':password', $pass_new, PDO::PARAM_STR );
            $data->bindParam( ':user', dvwaCurrentUser(), PDO::PARAM_STR );
            $data->execute();
    
            // Feedback for the user
            echo "<pre>Password Changed.</pre>";
        }
        else {
            // Issue with passwords matching
            echo "<pre>Passwords did not match or current password incorrect.</pre>";
        }
    }
    
    // Generate Anti-CSRF token
    generateSessionToken();
    
    ?>

可以看到，Impossible级别的代码利用PDO技术防御SQL注入，至于防护CSRF，则要求用户输入原始密码（简单粗暴），攻击者在不知道原始密码的情况下，无论如何都无法进行CSRF攻击。

# 4 CSRF漏洞修复建议 #

*  验证请求的Referer值，如果Referer是以自己的网站开头的域名，则说明该请求来自网站自己，是合法的。如果Referer是其他网站域名或空白，就有可能是CSRF攻击，那么服务器应拒绝该请求，但是此方法存在被绕过的可能。
 *  CSRF攻击之所以能够成功，是因为攻击者可以伪造用户的请求，由此可知，抵御CSRF攻击的关键在于:在请求中放入攻击者不能伪造的信息。例如可以在HTTP请求中以参数的形式加入一个随机产生的token，并在服务器端验证token，如果请求中没有token或者token的内容不正确，则认为该请求可能是CSRF攻击从而拒绝该请求。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70]: /images/20221123/21b60aef7c1c41a694bcf721e1265ba6.png
[http_192.168.1.100_dvwa_vulnerabilities_csrf_password_new_password_password_conf_password_Change_Change]: http://192.168.1.100/dvwa/vulnerabilities/csrf/?password_new=password&password_conf=password&Change=Change#
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 1]: /images/20221123/41705fae1e8440a89395522bd35d5013.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 2]: /images/20221123/c74d6353a133417db081c7f55d7581ba.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 3]: /images/20221123/1681f19910af464a85577f73320bee81.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 4]: /images/20221123/6380e26385cf49b5a74dcd3586cf92b7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0RyaWZ0ZXJfR2FsYXh5_size_16_color_FFFFFF_t_70 5]: /images/20221123/b87ae4569fdd48e7bc08f6ffed11a0da.png
[https_www.jianshu.com_p_4eed0faaf0ca]: https://www.jianshu.com/p/4eed0faaf0ca
[https_www.freebuf.com_articles_web_118352.html]: https://www.freebuf.com/articles/web/118352.html