Re: Overwriting an uninitialized local variable in PHP

["Tyler Krpata" <krpatasec () gmail com>]

Technically it's not "uninitialized" as you would think of in some
other languages. Variables in PHP that are not explicitly set have
default values.

Of course, and as usual, all bets are off if register_globals is enabled.

On 2/21/07, Kellox <kellox () my-mail ch> wrote:
> I'm addressing a PHP with a MySQL DB system.
>
> A PHP script looks like this:
>
> $sort_mode = $_GET['sort'];
> if($sort_mode = 'ascendend') $query = "....";
> else if($sort_mode = 'descendend') $query = "....";
> ...
> mysql_query($query) or die();
>
> This script does actually contain some serious problem because
> $sort_mode is not sanitized. But this variable is never used in a SQL
> query, so even if you modify the GET Parameter to become a SQL injection
> it won't be executed by the DB because this variable is not passed to
> the engine. The actual variable containing the query is $query. But
> since there's no else clause, $query is uninitialized, when you pass a
> string to the variable $sort_mode that is not contained in the
> if-then-else statement (e.g. $sort_mode = 'does_not_exist')
>
> My question is if there is a way to "initialize" the variable $query
> myself as an attacker from the outside, so that I can write my on SQL query.
>
> This question is related to a webapp review I'm doing at the moment.
>
> Thx in advance!

---------------------------------------------------------------------------
This list is sponsored by: BigFix

If your IT fails, you're out of business - or worse.  Arm your 
enterprise with BigFix, the single converged IT security and operations 
engine. BigFix enables continuous discovery, assessment, remediation, 
and enforcement for complex and distributed IT environments in real-time 
from a single console.
Think what's next. Think BigFix. 

http://ad.doubleclick.net/clk;82309979;15562032;o?http://www.bigfix.com/ITNext/
---------------------------------------------------------------------------