Facebook WhiteHat: Able to access group plan even after leaving the group. Product/URL : https://www.facebook.com/messages/t/[group_messagesID] Description and Impact Facebook messages has an option to create group, where a user can add multiple friends to chat, plan share pictures together. Whenever a user is not a part of the group, he is not allowed to see the updated information of the group. However one can still access the group plan even when not in a group. Peter, is it? Reproduction Instructions/Proof of Concept We have two test accounts, (test A) and (test B) 1. Test A Creates a new Group, Test Group, add members.(test B, test C ) 2. Test A creates a plan in group, with date, venue and plan name. 3. There is some argument between Test A and Test B, and Test B leaves the group. 4. Test A and Test C decides to change the plan venue as Test B was already aware of the all plan details. 5. Test A changes the plan venue and date, howev...