DVWA靶场之三：跨站请求伪造（CSRF）
CSRF（Cross-Site Request Forgery，跨站请求伪造）是一种让用户在不知情的情况下执行非本意操作的网络攻击。
生活化比喻
就像有人伪造你的签名：
你：银行客户（已登录网银）
攻击者：给你寄来一张"优惠申请表"
结果：你填表后，实际上是在授权转账给攻击者技术原理
攻击条件：
用户已登录目标网站（有会话cookie）
用户访问了恶意网站或邮件
恶意网站伪造请求到目标网站攻击流程：
1. 用户登录 bank.com ← 获得会话cookie
2. 用户访问 evil.com ← 恶意网站
3. evil.com 自动提交表单到 bank.com/transfer
4. 浏览器携带cookie发送请求 ← 银行认为是用户自愿操作
5. 转账完成！1. low难度
分析源码
php
<?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
$current_user = dvwaCurrentUser();
$insert = "UPDATE `users` SET password = '$pass_new' WHERE user = '" . $current_user . "';";
$result = mysqli_query($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);
}
?>源码里，只是通过pass_new == pass_conf 来通过两次相同输入新密码，并没有验证旧密码。而且用的GET方法，通过URL就可知道。
http://127.0.0.1/vulnerabilities/csrf/?password_new=123&password_conf=123&Change=Change#直接修改链接中的password_new和password_conf就能改密码了
2. medium难度
php
<?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
$current_user = dvwaCurrentUser();
$insert = "UPDATE `users` SET password = '$pass_new' WHERE user = '" . $current_user . "';";
$result = mysqli_query($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 : $___mysqli_res);
}
?>现在的代码：增加了 if( stripos($_SERVER['HTTP_REFERER'], $_SERVER['SERVER_NAME']) !== false )。
试图只接受来自本站的请求（简单的 Referer 白名单）。
在low 版本：没有任何 Referer 验证，任何带 ?Change=... 的请求都会被处理。
要绕过（medium 难度的防护），攻击者需要在发出的请求里人为加入 Referer 头，并且把它的来源（origin）写成正确的、被服务器接受的来源，这样应用就会把这个请求当作来自本站而处理。
这里可以使用burp，在request里添加referer数据
然后选择send，之后可以在reponse中看到密码被成功修改
3. high难度
php
<?php
$change = false;
$request_type = "html";
$return_message = "Request Failed";
if ($_SERVER['REQUEST_METHOD'] == "POST" && array_key_exists ("CONTENT_TYPE", $_SERVER) && $_SERVER['CONTENT_TYPE'] == "application/json") {
$data = json_decode(file_get_contents('php://input'), true);
$request_type = "json";
if (array_key_exists("HTTP_USER_TOKEN", $_SERVER) &&
array_key_exists("password_new", $data) &&
array_key_exists("password_conf", $data) &&
array_key_exists("Change", $data)) {
$token = $_SERVER['HTTP_USER_TOKEN'];
$pass_new = $data["password_new"];
$pass_conf = $data["password_conf"];
$change = true;
}
} else {
if (array_key_exists("user_token", $_REQUEST) &&
array_key_exists("password_new", $_REQUEST) &&
array_key_exists("password_conf", $_REQUEST) &&
array_key_exists("Change", $_REQUEST)) {
$token = $_REQUEST["user_token"];
$pass_new = $_REQUEST["password_new"];
$pass_conf = $_REQUEST["password_conf"];
$change = true;
}
}
if ($change) {
// Check Anti-CSRF token
checkToken( $token, $_SESSION[ 'session_token' ], 'index.php' );
// Do the passwords match?
if( $pass_new == $pass_conf ) {
// They do!
$pass_new = mysqli_real_escape_string ($GLOBALS["___mysqli_ston"], $pass_new);
$pass_new = md5( $pass_new );
// Update the database
$current_user = dvwaCurrentUser();
$insert = "UPDATE `users` SET password = '" . $pass_new . "' WHERE user = '" . $current_user . "';";
$result = mysqli_query($GLOBALS["___mysqli_ston"], $insert );
// Feedback for the user
$return_message = "Password Changed.";
}
else {
// Issue with passwords matching
$return_message = "Passwords did not match.";
}
mysqli_close($GLOBALS["___mysqli_ston"]);
if ($request_type == "json") {
generateSessionToken();
header ("Content-Type: application/json");
print json_encode (array("Message" =>$return_message));
exit;
} else {
echo "<pre>" . $return_message . "</pre>";
}
}
// Generate Anti-CSRF token
generateSessionToken();
?>和low难度相比，high难度有如下变化
加入 CSRF Token 验证，只有表单提交时带上正确的 token，服务器才会接受请求。避免了攻击者随便构造请求就能改密码。这和上一关的high难度很像，也是加了CSRF验证。
用burp抓包发现请求里带上了token
这里我们可以使用burpsuit的CSRF Token Tracker 插件绕过user_token验证。
CSRF Token Tracker 可以
自动提取 token：从 HTML（hidden input）、JSON、response header、meta、或脚本变量中抽取值（通常用正则或路径规则）。
自动注入 token：把提取出的 token 替换回发送的请求的指定位置（表单字段、JSON body、请求头等）。
输入主机名、token的名字和token的值
点击repeater里的send可以看到密码被修改成功。
4. impossible
php
<?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;' );
$current_user = dvwaCurrentUser();
$data->bindParam( ':user', $current_user, 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 );
$current_user = dvwaCurrentUser();
$data->bindParam( ':user', $current_user, 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();
?>修改密码之前需要验证原始密码，在攻击者不知道原始密码的基础上，是无法进行CSRF攻击的