PHP代码审计入门-DVWA靶场暴力破解篇

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五篇-DVWA靶场篇，对DVWA靶场漏洞进行代码审计。

0x01 暴力破解

暴力破解模块，注释写在代码里，尽量用详细的语言描述代码含义。

level-low

存在万能密码，可绕过用户名

low.php
<?php

if( isset( $_GET[ 'Login' ] ) ) {        //isset函数检测变量非空且设置
    // Get username
    $user = $_GET[ 'username' ];        //GET方式接收用户名

    // Get password
    $pass = $_GET[ 'password' ];        //GET方式接收密码
    $pass = md5( $pass );                //接收到的密码进行md5加密

    // Check the database
    $query  = "SELECT * FROM `users` WHERE user = '$user' AND password = '$pass';";
    //直接交互数据库，用户名存在万能密码

    /*var_dump($query);        //这里可以添加var_dump输出代码进行调式
    exit();*/

    $result = mysqli_query($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>' );
    //直接将SQL语句的执行结果显示给客户端
    if( $result && mysqli_num_rows( $result ) == 1 ) {
        //mysqli_num_rows()接受一个结果对象作为参数，检索返回给定结果的行数。实践见下图

        // Get users details
        $row    = mysqli_fetch_assoc( $result );
        //取一行比对
        $avatar = $row["avatar"];

        // Login successful
        $html .= "<p>Welcome to the password protected area {$user}</p>";
        $html .= "<img src=\"{$avatar}\" />";
        //成功输出xxx调用图片
    }
    else {
        // Login failed
        $html .= "<pre><br />Username and/or password incorrect.</pre>";
    }

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

?>
//为什么可以爆破，因为没用作任何限制

数据库users表单是五行数据，使用mysqli_num_rows()返回总共的行数

初级基本就这么多了

level-medium

这里相较于low，最大的区别点在于使用mysqli_real_escape_string()函数进行转义以防止恶意注入，所以万能密码登陆用不了了。

但有可能存在宽字节绕过，这与本身使用的php版本有关，可参考之前文章的第三十六关：

SQLI-labs靶场Less1-37详细学习记录（7400字总结）_身高两米不到的博客-CSDN博客

level-high

high和之前相比最大的区别点在于token认证

high.php
<?php

if( isset( $_GET[ 'Login' ] ) ) {
    // Check Anti-CSRF token
    checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );
    //调用checkToken
    // Sanitise username input
    $user = $_GET[ 'username' ];
    $user = stripslashes( $user );        //删除反斜杠，防注入的
    $user = ((isset($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
        $html .= "<p>Welcome to the password protected area {$user}</p>";
        $html .= "<img src=\"{$avatar}\" />";
    }
    else {
        // Login failed
        sleep( rand( 0, 3 ) );
        //随机slep0-3秒
        $html .= "<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();

?>

跟进到checkToken方法，设置三个参数，如果user_token不等于session_token或者session_token为空，调用dvwaRedirect方法。

跟进到dvwaRedirect，发现起到跳转作用

F12可以查看随机生成的token，token爆破绕过可以参考之前文章

level-impossiable

既然是impossibale，那以咱水平肯定绕不过去，直接看代码，代码对防注入方面使用了PDO预处理，对于爆破而言最狗的是设置次数。实际目标站点渗透可以死猜个用户名，然后弱密码隔断时间试试，至于hw还是早点溜了。

impossiable.php
<?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' ];        //改成POST提交账号密码
    $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 );
    //前面还是token，以及防注入的函数使用

    // Default values
    $total_failed_login = 3;            //登陆次数失败三次
    $lockout_time       = 15;            //等十五分钟
    $account_locked     = false;        //判断用户是否锁定

    // 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 );
    //使用PDO
    $data->execute();
    $row = $data->fetch();

    // Check to see if the user has been locked out.
    if( ( $data->rowCount() == 1 ) && ( $row[ 'failed_login' ] >= $total_failed_login ) )  {
        // User locked out.  Note, using this method would allow for user enumeration!
        //$html .= "<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
        $html .= "<p>Welcome to the password protected area <em>{$user}</em></p>";
        $html .= "<img src=\"{$avatar}\" />";

        // Had the account been locked out since last login?
        if( $failed_login >= $total_failed_login ) {
            $html .= "<p><em>Warning</em>: Someone might of been brute forcing your account.</p>";
            $html .= "<p>Number of login attempts: <em>{$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
        $html .= "<pre><br />Username and/or password incorrect.<br /><br/>Alternative, the account has been locked because of too many failed logins.<br />If this is the case, <em>please try again in {$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();

?>

关于PDO预编译防注入原理推荐文章：

奇安信攻防社区-SQL注入&预编译

0x02 总结

工作一年多重回校园，以打工人身份又转变到学生，这段时间开始忙碌，没有办法，作业考试太多。。。