MISP object edit authorization bypass allows unauthorized sharing group assignment

An authorization flaw in MISP’s object add/edit handling allowed an authenticated user with object editing permissions to assign a MISP object, or attributes contained within an object, to a sharing group that the user was not authorized to use or view. When editing objects, the sharing group validation was performed against the wrong request data structure after object fields had been merged to the top level, causing the check to be bypassed. In addition, attributes embedded in objects were not individually validated for authorized sharing group use. An attacker could craft a request with distribution set to 4 and an arbitrary sharing_group_id, potentially disclosing the existence or name of otherwise non-visible sharing groups and improperly modifying the distribution metadata of objects or contained attributes.