This situation comes into play when urldecode (or a similar function) is
called more than once - a common mistake, especially in PHP bulletin
boards.
$input_data = '%2527';
$input_data = urldecode($input_data); // causes it to become %27
// we do some other stuff and forget we already decoded it... or maybe
we merged new data that wasn't decoded so we decoded the whole thing
again - bad idea I know, but it could happen.
$input_data = urldecode($input_data);
// now we have a variable with one or more single quotes in it -
problem if we try to access a database with it, especially if it was
given to us maliciously.
If you look in the bugtraq archives at phpbb, invision, or vbulletin
you'll probably find one or more errors involving urldecode or similar
functions.
-Tony
mickael kael <mickael.kael@gmail.com> 06/25/05 08:35AM >>>
Hello,
Sorry to deviate the subject of the thread.
I see some code which use %2527 to bypass magic_quotes because %25
correspond to %. I try this technic with this code
(this is just a code for testing)
code : $sql = "SELECT nom FROM log where id='$id'";
url :
test.php?id=999%2527%20UNION%20ALL%20SELECT%20nom%20FROM%20log%20where%20id=1/*
result : SELECT nom FROM log where id='999%27 UNION ALL SELECT nom
FROM log where id=1/*'
But it don't work, i think, Mysql not interpret %27.
I read on the thread that it is possible to bypass magic_quotes, but i
don't find any solution. So if someone say it is possible, it will be
interessant to have a poc.
Thanks in advance,
Mk,
On 23 Jun 2005 08:30:59 -0000, maarten@webfauna.com
<maarten@webfauna.com> wrote:
I agree that magic quotes is not a very nice solution. Although it
makes it a little harder to manipulate queries, it will make your code
less clear. Some strings in you application are escaped (from POST data)
and some are not (e.g. from database.) Sometimes it's not completly
clear what the origin of a variable (string) is.
I think it's easier and safer if you can concider all strings to be
unescaped and make sure you escape them in a query.
You need clear and easy to understand code to make your application
secure.
In this case, I'd also use the intval() function. If you want an
integer value, this makes sure it is.
Greets,
Maarten
