Burpsuite/SQL Injection
From charlesreid1
This page contains notes on how to use Burp Suite to perform SQL injection attacks.
Burp Suite for SQL Injection
Burp Suite Workflow
The usual workflow when looking for SQL injection vulnerabilities looks something like this:
- start burp suite and open target site in burp proxy browser
- find a page or request containing a parameter that could be vulnerable to SQL injection
- turn on intercept, and intercept the request
- send the request to repeater
Now that you have the request in repeater, you can craft SQL queries and see the response from the server.
Repeater also has the ability to easily URL-encode plain text (Command-U will URL-encode the selected text), making SQL queries easier to craft.
Finding Vulnerable Site
Here is an example of an e-commerce website that is vulnerable to SQL injection:
The category=xyz parameter in the URL is the insecure portion of the application because it is not sanitized before being used in an SQL query.
Shortcut method to check if a parameter is vulnerable to SQL injection: try setting it to a single quote and see if the server returns an error.
(If so, it indicates that the underlying SQL query may have failed because of a syntax error, meaning user input is not escaped.)
Union Attacks
Link: https://portswigger.net/web-security/sql-injection/union-attacks
Procedure for carrying out a UNION attack:
- Determine the number of columns
- Determine the data types of columns
- Use this information to craft an attack
A UNION attack starts like most SQL injection attacks - with a single quote.
Start by finding the number of columns, by using ' UNION SELECT NULL, NULL-- or ' ORDER BY 1--'
You'll probably need to run this one a few times, with different numbers of NULL or column numbers, to figure out how many columns are returned by the vulnerable parameter.
Next, find columns with useful data types by modifying the SELECT query above to include a string type instead of a NULL type: ' UNION SELECT 'a',NULL,NULL,NULL--
We use the UNION SELECT payloads in this case. Trying with 1 or 2 NULL values returns a server error:
But once we try with 3 NULL values, the server successfully renders the page
Another Example: Order By, and Non-Microsoft SQL Server
MS SQL databases accept -- to start comments, but if it's not an MS SQL database, it may not accept the --. Instead, you need to use a hash sign to terminate the query early.
In this case, the procedure covered above needs to change slightly. Let's also cover how to use ORDER BY instead of SELECT NULL.
We start with the same vulnerable web application with its vulnerable "category" URL parameter:
/filter?category=xyz
Start out by browsing to that page in the Burp proxy. Turn on Intercept Traffic and refresh the page. You should now see the request for the /filter URL, with its "category" value set.
Now right click on this request, and send to repeater. Then you can turn off Intercept Traffic, and switch over to Repeater.
Here's what the un-tampered-with request might look like:
Now we can use the following SQL query in place of the category: ' ORDER BY 1--
(This will try to order the results that are being returned by the /filter URL by the first column. Increment to 2, 3, 4, etc. to discover how many columns the SQL query being attacked is returning.)
This request, when URL-encoded, is easy enough that we probably don't need Burp to do it for us: '+ORDER+BY+1--
However, in some cases, this will still return a 500 error:
In this case, we can try terminating the query string with a hash sign: ' ORDER BY 1 #
The hash sign must be URL-encoded, and Burp Suite will come in handy because it has built-in capabilities to obtain the URL-encoded version of a string.
When in repeater, and modifying the request URL, you can type the SQL query in a way that is NOT URL-encoded, and then select the text, and click Command-U to URL-encode the text.
Before:
After:
Once we send that request, we see the server return a 200 code, meaning we can continue on with our ORDER BY attacks to enumerate columns.
Determining Column Data Types
Example - Determine Data Type of Columns
Start with the same vulnerable e-commerce application, and still using the un-sanitized "category" variable. Start by repeating the attack shown above, to verify we are still dealing with the same number of columns:
/filter?category='+UNION+SELECT+NULL,NULL,NULL--
confirm that the page renders and does not return any error, indicating we are dealing with 3 columns:
Now we modify the query:
/filter?category='+UNION+SELECT+'a',NULL,NULL--
This returns an internal server error, so the first column is not a string type:
When we try the second column, the web application successfully renders the page, which means the second column returned is a string type:
/filter?category='+UNION+SELECT+NULL,'a',NULL--
The last column is not a string type either,
/filter?category='+UNION+SELECT+NULL,NULL,'a'--
Retrieving Data from Other Columns
Example - Retrieve Data from Other Columns
Start with the same e-commerce web application with the same SQL injection vulnerability in the category variable.
We start by repeating the two SQL injection attacks covered above, to verify that the products page is returning two fields, and that both fields are strings.
Now, we know that the products category page is fetching two string columns, and so we can do a UNION attack and fetch two other string columns. In this case, the username and password columns of the users table.
Craft the SQL injection query:
/filter?category='+UNION+SELECT+username,password+FROM+users--
This will create a query that is the union of usernames/passwords with the (empty) products query:
Retrieving Multiple Values in One Column
Example - Retrieving Multiple Values in One Column
Examining the Database
Querying the Database Type and Version
Example - Retrieving Database Version from Oracle
Example - Retrieving Database Version from MySQL and MS SQL
Working with the vulnerable web app with the category parameter that is vulnerable to SQL injection.
We start by finding the number of columns. In the process, we find that -- doesn't work as a statement-terminating sequence, but # does.
When we inject ' ORDER BY 1 # the application is ok
When we inject ' ORDER BY 2 # the application is ok
When we inject ' ORDER BY 3 # the application crashes, so there are 2 columns being returned
We can verify the columns being returned are text (which we can deduce from the UI, which has two text fields for each product) by injecting ' UNION SELECT 'a','a' #
This returns a 200, meaning there are 2 columns of text returned by the SQL query we are injecting
Last, we know that we can get the version of the server (https://charlesreid1.com/wiki/SQL_Injection/UNION_Attack#Querying_the_Database_Type_and_Version) by using SELECT @@version, but this returns a string with the version number, and we have to make two columns for the union query to work.
We inject the following query: ' UNION SELECT @@version,NULL #
This will put the version in one column and nothing in the other. This adds one more product to the bottom of the list of products, which contains the SQL server version number.
This sequence shows entering the injected query in plain text, then using Command-U to render it in URL encoding, then the resulting request (note the version number in the bottom right of the third image):
Resources
Links
Port Swigger Burp Suite training material:
- What is SQL injection? https://portswigger.net/web-security/sql-injection
- SQL injection union attacks: https://portswigger.net/web-security/sql-injection/union-attacks
- Examining the database: https://portswigger.net/web-security/sql-injection/examining-the-database
- Blind SQL injection: https://portswigger.net/web-security/sql-injection/blind
- Cheat sheet: https://portswigger.net/web-security/sql-injection/cheat-sheet
YouTube
SQL injection lab 7 - querying db type/version on oracle: https://www.youtube.com/watch?v=neeY0iVa_0A
SQL injection lab 8 - querying db type/version on mysql and ms sql: https://www.youtube.com/watch?v=MFTk_LNRW0g
YouTube
Helpful video covering the MySQL and MS SQL version vulnerabilities: https://www.youtube.com/watch?v=MFTk_LNRW0g