Symfony 2.0.6 has just been released. It addresses a security vulnerability in
EntityUserProvider as provided in the Doctrine bridge.
If you let your users update their login/username from a form, and if you are using Doctrine as a user provider, then you are vulnerable and you should upgrade as soon as possible.
The issue is that it is possible for a user to switch to another one. Here is how to reproduce it: The current user changes its username via a form to another existing username. When the form is submitted, he will have a validation error (as the username already exists) but the user object in the session will still be modified to the new username. This user from the session will be used for the next requests and so the user will be switched to this other user.
The fix is to always refresh the user via the primary key (which cannot be updated via a form) instead of the username.
If you cannot upgrade immediately, please apply the following patch: https://github.com/symfony/symfony/commit/9d2ab9ca9c1762
If you are starting a new project, you can get the Symfony Standard Edition distribution on the download page.
Then, run the vendors script:
$ ./bin/vendors install
And don't forget to clear your cache:
$ php ./app/console cache:clear
Remember that the Symfony2 Components are also available as standalone
libraries. You can get them via their dedicated read-only repositories on
https://github.com/symfony/Finder for instance), install them via
pear install symfony2/Finder), or even
install them via Composer.
As we've stated in the past, please report security-related issues to security [at] symfony-project [dot] com rather than posting them directly to Github. This will give the core team the opportunity to review and address the issue before word gets out.