pike-php at kw dot nl (2011-02-07 06:00:29)

When accidently assigning a unset variable to $_SESSION, like
$_SESSION['foo'] = $bar
while $bar was not defined, I got the following error message:
"Warning: Unknown(): Your script possibly relies on a session side-effect which existed until PHP 4.2.3. Please be advised that the session extension does not consider global variables as a source of data, unless register_globals is enabled. "
The errormessage was quite unrelated and got me off-track. The real error was, $bar was not defined.

Dave (2009-11-17 14:05:47)

If you deploy php code and cannot control whether register_globals is off, place this snippet in your code to prevent session injections:

<?php
if (isset($_REQUEST['_SESSION'])) die("Get lost Muppet!");
?>

charlese at cvs dot com dot au (2009-07-04 18:47:26)

I was having troubles with session variables working in some environments and being seriously flaky in others. I was using $_SESSION as an array. It works properly when I used $_SESSION as pointers to arrays. As an example the following code works in some environments and not others.

<?php
//Trouble if I treate $form_convert and $_SESSION['form_convert'] as unrelated items
$form_convert=array();
if (isset($_SESSION['form_convert'])){
        $form_convert=$_SESSION['form_convert'];
    }
}
?>
The following works well. 
<?php
if (isset($_SESSION['form_convert'])){
    $form_convert = $_SESSION['form_convert'];
}else{
    $form_convert = array();
    $_SESSION['form_convert']=$form_convert;
}
?>

bohwaz (2008-08-31 14:43:37)

Please note that if you have register_globals to On, global variables associated to $_SESSION variables are references, so this may lead to some weird situations.

<?php

session_start();

$_SESSION['test'] = 42;
$test = 43;
echo $_SESSION['test'];

?>

Load the page, OK it displays 42, reload the page... it displays 43.

The solution is to do this after each time you do a session_start() :

<?php

if (ini_get('register_globals'))
{
    foreach ($_SESSION as $key=>$value)
    {
        if (isset($GLOBALS[$key]))
            unset($GLOBALS[$key]);
    }
}

?>

Steve Clay (2008-08-17 06:28:18)

Unlike a real PHP array, $_SESSION keys at the root level must be valid variable names.

<?php 
$_SESSION[1][1] = 'cake'; // fails

$_SESSION['v1'][1] = 'cake'; // works
?>

I imagine this is an internal limitation having to do with the legacy function session_register(), where the registered global var must similarly have a valid name.

jherry at netcourrier dot com (2008-08-01 16:16:05)

You may have trouble if you use '|' in the key:
$_SESSION["foo|bar"] = "fuzzy";
This does not work for me. I think it's because the serialisation of session object is using this char so the server reset your session when it cannot read it.
To make it work I replaced '|' by '_'.