MySQL trick for SQL injection

[Vladimir Vorontsov <vladimir.vorontsov () onsec ru>]

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

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Best regards!
Vladimir Vorontsov, security expert.
ONsec: turn on security

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