CSRF 跨站请求伪造介绍
跨站请求伪造 (Cross-Site Request Forgery, CSRF),也被称为 One Click Attack 或者 Session Riding ,通常缩写为CSRF,是一种对网站的恶意利用。通常利用受害者尚未失效的身份认证信息(cookie、会话等),诱骗其点击恶意链接或者访问包含攻击代码的页面,在受害者不知情的情况下以受害者的身份向服务器发送请求,从而完成非法操作(改密)。CSRF与XSS最大的区别在于,CSRF并没有盗取cookie而是直接利用。
CSRF(low)
进入CSRF,修改密码为123
修改成功,可以看到链接为get请求,其中中包含了我们要修改的密码,当然我们可以更改其中的参数
http://192.168.115.130:89/vulnerabilities/csrf/?password_new=123&password_conf=123&Change=Change#
更改新的密码为123456,在浏览器复制以下链接,直接将密码修改成123456
http://192.168.115.130:89/vulnerabilities/csrf/?password_new=123456&password_conf=123456&Change=Change#
需要注意的是,必须使用之前登录的浏览器打开链接才能修改成功。所以CSRF攻击的前提是目标网站存在CSRF,而且受害者需要保持目标站点的登录活动状态,还需要点击钓鱼链接。
CSRF攻击的改进:
1、生成短链接
2、将CSRF代码嵌入其他网页
<img src="http://192.168.115.130:89/vulnerabilities/csrf/?password_new=1234&password_conf=1234&Change=Change#" border="0" style="display:none;"/>
<h1>404<h1>
<h2>file not found.<h2>
代码分析:low级别的CSRF源码,利用mysql_real_escape_string()函数对$pass_new
和$pass_conf
变量进行了过滤,可以防止SQL注入,但无法阻止CSRF攻击。
<?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 : $___mysqli_res);
}
?>
CSRF(medium)
代码分析:
medium级别的CSRF源码,在获取$pass_new
和$pass_conf
两个变量之前,先利用if语句以及eregi()函数来判断"$_SERVER['HTTP_REFERER']"
的值是否是主机ip。
stripos()函数查找字符串在另一个字符串中第一次出现的位置(不区分大小写),如何没有找到返回false。
<?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);
}
?>
小笔记:HTTP头中的Referer字段,记录了该HTTP请求的来源地址
上述过滤规则是http的Referer参数的值中必须包含主机名,可以将攻击页面命名为ip.html(页面被放置在攻击者的服务器里)就可以绕过了
CSRF(high)
high级别的代码增加了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,才会处理客户端请求。
<?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();
?>
只有获取token才能进行CSRF,但是浏览器的跨域问题,不能直接获取,所以比较难利用。但是如果服务器存在存储XSS可以来获取token, 然后构造url和代码进行CSRF利用。所以high级别的CSRF将会组合存储XSS一起利用。
CSRF(impossible)
与之前不同的是,要求输入当前密码的才能修改密码,进行过滤,使用了PDO避免SQL注入,判断当前密码输入正确且修改的密码一致时才能生成新的密码
// 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();
常见防范措施
1、加入Anti-CSRF,每次向客户端发送一个随机数,当客户端向服务器发送数据时对比随机数从而确定身份
2、获取当前用户密码,以此判断是否为当前用户操作
3、二次确认(提示、二次密码、验证码)