End-to-end encryption is the major security feature of secure instant messengers, among the most popular one is WhatsApp having more than one billion users.
Security researchers discovered vulnerabilities with Whatsapp and Signal which allows an attacker to add themselves to the group chat. But the risk associated with the attack is limited.
Researchers say that ???if anyone that control over the WhatsApp???s servers could add new users to the WhatsApp group without the administrator permission???, it also affect signal and Threema but the impact is less.