An outsider can secretly listen everything on your private end-to-end encryption chats on WhatsApp. End-to-end encryption plays a important role in three types- malicious user, network attacker and malicious server,-- in securing instant messaging services.
The primary purpose of end-to-end encryption is to stop trusting on the server connected between the network. So, nobody can decrypts your messages, even no company decrypts your messages who transmit the data. It's all the things done to keep your identity private.
But Ruhr-Universitat Bochum (RUB) Researchers from Germany founds that anyone who controls the WhatsApp server signals can add a new member on any private group who steals all the conversation without the permission of the admin.
As described by the Researchers, the conversation of two persons is fully encrypted and servers plays very limited role but in case of multi peoples conversation like multi-broadcasting and the encrypted messages send to all the users of that group so, that's why servers plays major role.
Here's the big issue rise that any corrupted company can see any message of the private group without the permission of the admin. They can add any person to the group who steals all the chats of the group.