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SQL Injection Basic Union Based Injection. In this tutorial we will learn how to inject Union based injection.

In our last tutorial we learnt how to find out the number of columns used under the query so that we can use Union select statement. So we will continue that same url and same injection we were injecting. In the last tutorial we found that the vulnerable URL is having 5 numbers of columns and the below query was working.

Now we will use Union select statement over here.

what will it do is concatenate one more row to the output which will look like this

column1 column2 column3 column4 column5
anydata anydata anydata anydata anydata
1 2 3 4 5

Here a small understanding of the web application is required, If you see any of these numbers printed in the webpage or the title or anywhere else then you can know the the developer is printing multiple rows. But in case you can not see any of these numbers printed then you can simply invalidate the first query so that it wont give any output and eventually your output will become the one and only output to be printed.

Above i have specified some ways to make a query invalid but remember that & should be url encoded before usage. Now when we will use any of the above query, one row will come in output.

column1 column2 column3 column4 column5
1 2 3 4 5

Any of the number must be printed in the webpage again as basic thing to understand is that programmer may be only printing some particular columns from the output, lets say the third one. So we if we can see 3 in the page then its good otherwise we can try the query below with some other values.

Now just try to find it inside the source code. If you find hello1 that means the first colums is getting printed and if you found hello2 then the second column is getting printed and so on. Still some times if the programmer is using mysql_real_escape_string it may create an error or else no output. We can simply avoid the usage of single quotes using hex values. Below is the encoded query for the above same query.

One small thing to remember is that always add 0x before any hexadecimal value. Hopefully the above query should work and you will find the column which is getting printed on the webpage or inside the source code. We will stich up with 3rd column for this example. As we know that any thing on place of third column is getting printed. Then now we can try some Default functions and variables, to get some information related to our target. Below are some of the Variables/Functions that can be used to get information about your target machine.

Variable/Function Output
@@hostname : Current Hostname
@@tmpdir : Tept Directory
@@datadir : Data Directory
@@version : Version of DB
@@basedir : Base Directory
user() : Current User
database() : Current Database
version() : Version
schema() : current Database
UUID() : System UUID key
current_user() : Current User
current_user : Current User
system_user() : Current Sustem user
session_user() : Session user
@@GLOBAL.have_symlink : Check if Symlink Enabled or Disabled
@@GLOBAL.have_ssl : Check if it have ssl or not

As we know that third is the column which is getting printed so now we will use the above functions on place of that columns only.

Now we will move to our next part, which is Data Extraction.

Data Extraction using SQLi

There are many ways to extract data using SQLi so first one is union based. First i will show you the Queries and then show you how we can inject them.

Will give us names of all the Databases avaiable. But as we found earlier that sometimes programmer may not be printing all the rows. He may be printing the first row from output. So in that case we can use limit keyword to enumerate the rows one by one.

In the above manner we can get each row one by one. Now lets see how can we extract all the table names from a database.

Above injection will give you all the rows at once, but if you want one by one then you can use limit.

After getting the Table Names we can move on and start collecting the names of Columns under any table. we can specify the table name as we have all the tablenames.

If the above query do not give any output or an error. You can try to hex the tablename. And now we can try to get all the table names one by one if only one row is getting printed.

Now we know the database name, the table names and the column names so the last stage starts of extracting data from the columns. Now we have to specify from which column we want the data and from which table. Query and injection is simple at this stage

Thats all for Basic Union Based Injection.

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