Learning Web Pentesting With DVWA Part 2: SQL Injection

In the last article Learning Web Pentesting With DVWA Part 1: Installation, you were given a glimpse of SQL injection when we installed the DVWA app. In this article we will explain what we did at the end of that article and much more.

Lets start by defining what SQL injection is, OWASP defines it as: "A SQL injection attack consists of insertion or "injection" of a SQL query via the input data from the client to the application. A successful SQL injection exploit can read sensitive data from the database, modify database data (Insert/Update/Delete), execute administration operations on the database (such as shutdown the DBMS), recover the content of a given file present on the DBMS file system and in some cases issue commands to the operating system. SQL injection attacks are a type of injection attack, in which SQL commands are injected into data-plane input in order to effect the execution of predefined SQL commands."

Which basically means that we can use a simple (vulnerable) input field in our web application to get information from the database of the server which hosts the web application. We can command and control (at certain times) the database of the web application or even the server.

In this article we are going to perform SQL injection attack on DVWA, so let's jump in. On the DVWA welcome page click on SQL Injection navigation link. We are presented with a page with an input field for User ID.

Now lets try to input a value like 1 in the input field. We can see a response from server telling us the firstname and surname of the user associated with User ID 1.

If we try to enter a user id which doesn't exist, we get no data back from the server. To determine whether an input field is vulnerable to SQL injection, we first start by sending a single quote (') as input. Which returns an SQL error.

We saw this in the previous article and we also talked about injection point in it. Before diving deeper into how this vulnerability can be exploited lets try to understand how this error might have occurred. Lets try to build the SQL query that the server might be trying to execute. Say the query looks something like this:

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

The 1 in this query is the value supplied by the user in the User ID input field. When we input a single quote in the User ID input field, the query looks like this:

SELECT first_name, sur_name FROM users WHERE user_id = '''; 

The quotes around the input provided in the User ID input field are from the server side application code. The error is due to the extra single quote present in the query. Now if we specify a comment after the single quote like this:
'-- -
or
'#
we should get no error. Now our crafted query looks like this:

SELECT first_name, sur_name FROM users WHERE user_id = ''-- -'; 

or

SELECT first_name, sur_name FROM users WHERE user_id = ''#'; 

since everything after the # or -- - are commented out, the query will ignore the extra single quote added by the server side app and whatever comes after it and will not generate any error. However the query returns nothing because we specified nothing ('') as the user_id.

After knowing how things might be working on the server side, we will start to attack the application.
First of all we will try to determine the number of columns that the query outputs because if we try a query which will output the number of columns greater or smaller than what the original query outputs then our query is going to get an error. So we will first figure out the exact number of columns that the query outputs and we will do that with the help of order by sql statement like this:

' order by 1-- - 

This MySQL server might execute the query as:

SELECT first_name, sur_name FROM users WHERE user_id = '' order by 1-- -'; 

you get the idea now.
if we don't get any error message, we will increase the number to 2 like this:

' order by 2-- - 

still no error message, lets add another:

' order by 3-- - 

and there we go we have an error message. Which tells us the number of columns that the server query selects is 2 because it erred out at 3.

Now lets use the union select SQL statement to get information about the database itself.

' union select null, version()-- - 

You should first understand what a union select statement does and only then can you understand what we are doing here. You can read about it here.
We have used null as one column since we need to match the number of columns from the server query which is two. null will act as a dummy column here which will give no output and the second column which in our case here is the version() command will output the database version. Notice the output from the application, nothing is shown for First name since we specified null for it and the maria db version will be displayed in Surname.
Now lets check who the database user is using the user() function of mariadb:

' union select null, user()-- - 

After clicking the submit button you should be able to see the user of the database in surname.

Now lets get some information about the databases in the database.
Lets determine the names of databases from INFORMATION_SCHEMA.SCHEMATA by entering following input in the User ID field:

' union select null, SCHEMA_NAME from INFORMATION_SCHEMA.SCHEMATA-- - 

This lists two databases dvwa and information_schema. information_schema is the built in database. Lets look at the dvwa database.
Get table names for dvwa database from INFORMATION_SCHEMA.TABLES

' union select null, TABLE_NAME from INFORMATION_SCHEMA.TABLES-- - 

It gives a huge number of tables that are present in dvwa database. But what we are really interested in is the users table as it is most likely to contain user passwords. But first we need to determine columns of that table and we will do that by querying INFORMATION_SCHEMA.COLUMNS like this:

' union select null, COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'users'-- - 

We can see the password column in the output now lets get those passwords:

' union select user, password from users-- - 

Of-course those are the hashes and not plain text passwords. You need to crack them.
Hope you learned something about SQL injection in this article. See you next time.

References:

1. SQL Injection: https://owasp.org/www-community/attacks/SQL_Injection
2. MySQL UNION: https://www.mysqltutorial.org/sql-union-mysql.aspx
3. Chapter 25 INFORMATION_SCHEMA Tables: https://dev.mysql.com/doc/refman/8.0/en/information-schema.html

More information

1. Pentest Tools Find Subdomains
2. Hacking Tools Pc
3. Hacking Tools Download
4. Blackhat Hacker Tools
5. Pentest Tools For Windows
6. Pentest Tools Apk
7. Hack Tools Download
8. Pentest Tools For Mac
9. Pentest Automation Tools
10. Pentest Tools Website
11. Android Hack Tools Github
12. Hacker Tools Software
13. Hacking Tools For Beginners
14. Hack Tool Apk
15. Hacker Tool Kit
16. Hacker Tools Hardware
17. Hack Tools For Ubuntu
18. Pentest Tools Nmap
19. Hak5 Tools
20. Bluetooth Hacking Tools Kali
21. Hacking Tools Free Download
22. Hack Tools Pc
23. Hacking Tools Windows
24. Hacker Tools Apk Download
25. Hack Apps
26. Hacker Tools Hardware
27. Hacker Tools For Pc
28. Hacks And Tools
29. New Hacker Tools
30. Hack Tools For Games
31. Hack Tools Download
32. Hacker Tools For Mac
33. Hacking Apps
34. Hack App
35. Nsa Hack Tools
36. Hacking Tools For Pc
37. Hack Tool Apk No Root
38. Hack Tools Download
39. Android Hack Tools Github
40. Pentest Tools Review
41. Pentest Tools Download
42. Hack Tools For Mac
43. Android Hack Tools Github
44. Hacker
45. Hacker Hardware Tools
46. Hacker Tools Linux
47. Hacker Tools For Windows
48. Hack App
49. Hacking App
50. Pentest Tools Open Source
51. Hack App
52. Best Hacking Tools 2019
53. Hacking Tools For Pc
54. Github Hacking Tools
55. Hacking App
56. Computer Hacker
57. Hacker Security Tools
58. Usb Pentest Tools
59. Pentest Tools Subdomain
60. Github Hacking Tools
61. Pentest Tools Port Scanner
62. Bluetooth Hacking Tools Kali
63. Hacker Tool Kit
64. How To Hack
65. Hack Tools For Games
66. Nsa Hack Tools
67. Hacking Tools Name
68. New Hack Tools
69. What Is Hacking Tools
70. Pentest Tools Github
71. Nsa Hacker Tools
72. Hacker
73. Hack Rom Tools
74. Pentest Tools Alternative
75. Hacker Tools For Ios
76. Beginner Hacker Tools
77. Pentest Tools Tcp Port Scanner
78. Hack Tool Apk No Root
79. Growth Hacker Tools
80. Hack Tools For Pc
81. Hacker Tools List
82. Pentest Automation Tools
83. Ethical Hacker Tools
84. Best Hacking Tools 2019
85. Hacker Hardware Tools
86. New Hack Tools
87. Pentest Tools Download
88. How To Hack
89. Pentest Tools Website
90. Pentest Tools Kali Linux
91. Hack Website Online Tool
92. Termux Hacking Tools 2019
93. Hack Tools Mac
94. Pentest Tools Download
95. Black Hat Hacker Tools
96. Hackrf Tools
97. Hacking Tools Usb
98. Hacker Tools 2020
99. Hacking Tools For Windows Free Download
100. New Hack Tools
101. Pentest Automation Tools
102. Hack Tools Online
103. Pentest Tools Find Subdomains