How to secure pass and set session id?

Question

I'm using uploadify and the script (which uses adobe flash) creates a new session instead of using the current one when requesting the upload action url. To fix that I need to pass ahead the session id.

Is there a way to do this without permit session fixation (hijacking)?

Here are some details of the problem: Sessions and uploadify

Thanks!

Answer 1

Create a temporary upload session in your script (untested, but you get the point about being able to have several different sessions):

<?php
//normal session
session_start();
//store sessionid for retrieval
$oldsessionid = session_id();
if($_SESSION['logged_in']){ //or however you check for a valid user
    //stop old/normal session
    session_write_close();   
    //create a new sessionname
    $oldname = session_name('UPLOADSESSION');
    //create a new id (fixed here, you might want a random number/char combo:
    session_id('myuploadsessionid');
    //start the session
    session_start();
    $_SESSION['upload'] = true;
    $uploadid = session_id();
    //now you can use `'data: "artist="+$fi+"&UPLOADSESSION="'.$uploadid` in uploadify
    session_write_close();
}
//return to normal name
session_name($oldname);
//set old session id
session_id($oldsessionid);
//resume normal session
session_start();

So, in your receiving script:

<?php
session_name('UPLOADSESSION');
session_id($_POST['UPLOADSESSION']);
session_start();
if(isset($_SESSION['upload']) && $_SESSION['upload']){
   //accept files
   //invalidate session after this upload
   $_SESSION['upload'] = false;
}

The user will still have 2 cookies, and possibly UPLOADSESSION is fixated, but you don't use it for anything else then uploading, and only for 1 upload (although you might want to allow more).

Alternatively, you could just call a session_regenerate_id(); on the first request after an upload (just set a flag in the $_SESSION on upload).