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Bug #51120 If session var is NULL, value will be overwritten by global with same name
Submitted: 2010-02-23 08:30 UTC Modified: 2010-02-23 18:57 UTC
From: antonio04 at gmail dot com Assigned:
Status: Not a bug Package: Session related
PHP Version: 5.3.1 OS: FreeBSD 7.2
Private report: No CVE-ID: None
View Developer Edit
 [2010-02-23 08:30 UTC] antonio04 at gmail dot com 
Description:
------------
When you have a session variable whose whose session array key is 
defined but with a NULL value, this variable acts as if register_globals 
were enabled, i.e. any value set to a global variable of the same name 
is stored in the session as this key's value.

Once the session variable's value has been changed to something not 
null, this behavior ceases.

A cursory search in the archives shows that this issue was categorized 
as a bogus bug report six years ago (#28482), but the reason given does 
not make sense, as the session variable key certainly does exist and 
acts unexpectedly when initialized to NULL.

Thanks!

Reproduce code:
---------------
<?php
/* Script 1 */
session_start();
init_set('register_globals', 0);
$_SESSION['foo'] = NULL;
$foo = 'bar';
?>

<?php
/* Script 2 */
session_start();
var_dump($_SESSION['foo']);
?>

Expected result:
----------------
Script 1: 

Script 2: 
Notice: Undefined index: foo in /home/www/interpals/test.php on line 3
NULL

Actual result:
--------------
Script 1:

Script 2:
string(3) "bar"

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 [2010-02-23 08:42 UTC] antonio04 at gmail dot com 
Sorry, there was a typo in the reproduce code -- please check this 
instead:

<?php
/* Script one */
ini_set('register_globals', 0);
session_start();
$_SESSION['foo'] = NULL;
$foo = 'bar';
?>

Then view the second script:
<?php
/* Script two */
session_start();
var_dump($_SESSION['foo']);
?>
 [2010-02-23 10:33 UTC] antonio04 at gmail dot com 
Here are the expected/actual results: 

Expected result:
----------------
Script 1: 

Script 2: 
NULL

Actual result:
--------------
Script 1:

Script 2:
string(3) "bar"
 [2010-02-23 12:55 UTC] jani@php.net 
For starters, you can't set register_globals in script. Hence there's no bug but expected (bad) behaviour on having register_globals = On. Switch it off and all is well. :)
 [2010-02-23 13:07 UTC] antonio04 at gmail dot com 
Thanks for your quick response.

Sorry, I should have mentioned that register_globals is off in php.ini.  
I included the ini_set line to illustrate that point, but I suppose 
that's moot, since you can't set it via ini_set =)

However, the problem is still there... can you please try to reproduce 
it?
 [2010-02-23 13:13 UTC] antonio04 at gmail dot com 
Just to confirm, register_globals is definitely off -- both as reported 
by phpinfo() as well as the following snippet:

<?php
echo 'register_globals = ' . ini_get('register_globals') . "\n";
?>

Which displays the following: 

register_globals =
 [2010-02-23 18:57 UTC] antonio04 at gmail dot com 
On further research, this seems due to the session.bug_compat_42 
bug/"feature".  Turning this setting off in php.ini has resolved the 
issue. Thanks.
 
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