Re: MySQL trick for SQL injection

[Paul Schmehl <pschmehl_lists () tx rr com>]

--On Friday, November 06, 2009 06:55:22 -0600 Vladimir Vorontsov 
<vladimir.vorontsov () onsec ru> wrote:

> Good day!
>
> I recently encountered a problem with the implementation of SQL injection.
>
> I wanted to write a file with the code interpreter to execute commands, but
> in the end always append bracket, which I thought was supposed to be a
> spoiler.
>
> Comments at the end of the query to be filtered. The last character is
> always append a closing parenthesis. Use a null-byte, too, was impossible.
>
> Was an injection of this type:
>
> $query = "select bla-bla from content_comments where user_id in (select
> user_id from User where id =".removeBadChars($_GET['id']).");";
> Where removeBadChars () kills such things as:
> --
> /*
> but leaves /**/
> I wanted to write a script to execute commands in a file. The rows included
> in the first select, but the presence of brackets before inkludom demanded
> its closure after it. Besides tricky function is not allowed to finish a
> comment form - or /* at the end of the query.
>
> As a result, very surprised, because that's such an option:
>
> select bla-bla from content_comments where user_id in (select user_id from
> User where id = 1/**/into/**/outfile/**/"/var/www/avatars/img.php")
>
> recorded in the file the result of EXTERNAL select!.
>
> Checked in
> MySQL 4.1.22
> MySQL 5.1.x

What privileges did the user who performed the select have?

INTO OUTFILE is a dangerous routine (as you've clearly demonstrated), but that 
privilege must be specifically granted to a user before it's possible to 
execute it.  No sensible administrator would grant the FILE privilege to a 
webserver application's database acccount.  (Usually SELECT, INSERT, and UPDATE 
should be enough.)

OTOH, if you've found a way to execute FILE without having that privilege 
granted to the account, you've uncovered a serious problem.

-- 
Paul Schmehl, Senior Infosec Analyst
As if it wasn't already obvious, my opinions
are my own and not those of my employer.
*******************************************
"It is as useless to argue with those who have
renounced the use of reason as to administer
medication to the dead." Thomas Jefferson

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