PHP代码审计入门-DVWA靶场CSRF篇

0x00 写在前面

从零学习php，最终目的实现代码审计入门，软件采用sublime text，环境使用phpstudy搭建，数据库是navicat，需要有基本的前端基础、简单的php+mysql后端基础、渗透知识和漏洞原理，文章跟随流沙前辈学习记录，看看曾经遥不可及的代码审计能不能慢慢啃下来。

本章为代码审计入门第七篇-DVWA靶场篇，对DVWA靶场漏洞进行代码审计。

0x01 CSRF

CSRF模块，注释写在代码里，尽量用详细的语言描述代码含义。

level-low

low.php

<?php

if( isset( $_GET[ 'Change' ] ) ) {
	// Get input
	//设置并非空，GET型传参
	$pass_new  = $_GET[ 'password_new' ];
	$pass_conf = $_GET[ 'password_conf' ];
	//接收用户输入
	// Do the passwords match?
	if( $pass_new == $pass_conf ) {
		// They do!
		//两次值相同
		$pass_new = ((isset($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 );
		// 用mysqli_real_escape_string做一次简单过滤，给新密码进行一次加密
		// Update the database
		$insert = "UPDATE `users` SET password = '$pass_new' WHERE user = '" . dvwaCurrentUser() . "';";
		//更新数据库密码
		$result = mysqli_query($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
		$html .= "<pre>Password Changed.</pre>";
	}
	else {
		// Issue with passwords matching
		$html .= "<pre>Passwords did not match.</pre>";
	}

	((is_null($___mysqli_res = mysqli_close($GLOBALS["___mysqli_ston"]))) ? false : $___mysqli_res);
}

?>

更新数据库代码部分有一个函数dvwaCurrentUser，跟进看代码逻辑。

又发现一个 &dvwaSessionGrab，继续跟进

然后产生疑惑， &dvwaSessionGrab函数为什么要加& ，百度一番没看懂，吐槽一下：他喵的就不能用朴实无华的语言写出来，非得装杯。。。。。

好的，文章内容代码不是重点，重点是逻辑和漏洞。总结其方法的代码逻辑是判断用户是否登陆，如果用户已登陆把登陆的username返回来，然后修改其数据库对应的password。

为什么会产生漏洞？因为什么限制也没做。

level-medium

相比于low增加一个验证功能，作用简单讲就是检验referer和host值能否匹配上，也就是判断该头的主机地址是否来自DVWA，是继续不是拜拜。

medium.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
		//stripos函数检测[ 'SERVER_NAME' ]在[ 'HTTP_REFERER' ]出没出现，出现下一步没出现false
		$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
			$html .= "<pre>Password Changed.</pre>";
		}
		else {
			// Issue with passwords matching
			$html .= "<pre>Passwords did not match.</pre>";
		}
	}
	else {
		// Didn't come from a trusted source
		$html .= "<pre>That request didn't look correct.</pre>";
	}

	((is_null($___mysqli_res = mysqli_close($GLOBALS["___mysqli_ston"]))) ? false : $___mysqli_res);
}

?>

为什么有漏洞，因为burp抓包修改referer和host值就可以

level-high

相比于之前增加token认证，校验浏览器随机产生的token和用户提交修改密码时的token是否一致。其实感觉正常情况，基本有token机制就已经很难实现csrf了。

high.php

<?php

if( isset( $_GET[ 'Change' ] ) ) {
	// Check Anti-CSRF token
	checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );
	// token验证
	// 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
		$html .= "<pre>Password Changed.</pre>";
	}
	else {
		// Issue with passwords matching
		$html .= "<pre>Passwords did not match.</pre>";
	}

	((is_null($___mysqli_res = mysqli_close($GLOBALS["___mysqli_ston"]))) ? false : $___mysqli_res);
}

// Generate Anti-CSRF token
generateSessionToken();

?>

但是这里结合XSS还是存在风险的

漏洞组合拳之XSS+CSRF记录 - FreeBuf网络安全行业门户

level-impossible

既然是impossibale，那以咱水平肯定绕不过去，直接看代码。

代码做了PDO防注入，对于防csrf来讲，最大的区别在于代码要求用户输入原密码，不知道原密码也就不能进行csrf攻击了。

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;' );
	$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
		$html .= "<pre>Password Changed.</pre>";
	}
	else {
		// Issue with passwords matching
		$html .= "<pre>Passwords did not match or current password incorrect.</pre>";
	}
}

// Generate Anti-CSRF token
generateSessionToken();

?>