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.

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Centralized Messaging Servers

Security Instant messaging apps should satisfy general security goals and the group messages also should have the same measures.

Security researchers said the confidentiality is broken as soon as the uninvited member can obtain all the new messages and read them,” says Paul Rösler, one of the Ruhr University researchers who co-authored a paper on the group messaging vulnerabilities. Reported Wired.

Instant Security messengers use centralized authentication and all the messages transferred through a central server that receives catches and forwards messages.

Vulnerability Impact – WhatsApp flaw

Researchers say both the Whatsapp and Signal failed to Authenticate group messages, the Vulnerability allows an attacker who controls the WhatsApp server or breaks into Transport layer can get full control over a group.

With Signal everyone in the group is an administrator every one in the group can add new users “Researchers discovered the signal management doesn’t check that you are the member of the group before adding a new user”.
In WhatsApp only the administrator authorized to add users and to management messages and it is no signed by administrators, “so the malicious WhatsApp server or if the attacker has control over WhatsApp server can add new users”.

Fix Suggested by researchers

The signal could reach Traceable Delivery by treating receipt messages like content messages and thus end-to-end encrypt them.

Researchers suggested WhatsApp for providing Traceable Delivery by signing the messages with the administrator’s group signature key.

In Threema there is already a message ID appended to every message, this ID only needs to be cryptographically bound to the message.

Researchers Concluded, “We fill this gap by providing a security model and a methodology for analyzing group instant messaging protocols“.

While our investigation focuses on three major instant messaging applications, our methodology, and the underlying model is of generic purpose and can be applied to other secure groups instant messaging protocols as well.

Researchers from Ruhr University Bochum in Germany published the paper in at the At the Real World Crypto security conference.


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