inc/central.class.php in GLPI before 0.84.2 does not attempt to make install/install.php unavailable after an installation is completed, which allows remote attackers to conduct cross-site request forgery (CSRF) attacks, and (1) perform a SQL injection via an Etape_4 action or (2) execute arbitrary PHP code via an update_1 action.
The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.