ZF2015-01: Session validators were not run if set before session start.
Essentially, the validators were writing to the $_SESSION superglobal before
session start, which meant the data was overwritten once the session began.
This meant on subsequent calls, the validators had no data to compare against,
making the sessions automatically valid. We have provided patches to ensure
that validators are run only after the session has begun, which will ensure
they validate sessions correctly going forward. If you use Zend\Session
validators, we recommend upgrading immediately.