WhatsApp group chats not as secure as users might believe

Researchers have discovered flaws in the way WhatsApp,is messaging app handle secure (encrypted) group communication,which could result in unauthorized users getting added to closed groups and monitoring future conversations within them.

The problem with WhatsApp:
Paul Rösler, Christian Mainka, and Jörg Schwenk analysed the three widely used protocols and their implementations, and found that if someone – e.g., nation-state backed hackers (illegally), or law enforcement or intelligence agencies (legally) – gains control of WhatsApp’s servers, they could easily insert a new member in a private group without the permission of the group’s administrator(s).

The other participants will get a notification about a new user joining the group, but they have no way of knowing whether the new member was invited by the administrator(s). Also, if the attacker controls the server, he or she can block the messages sent by users who might question the new addition or warn others about it.

As noted cryptographer and Johns Hopkins University professor Matthew Green explained, the vulnerability stems from the fact that the WhatsApp server plays a significant role in group management, and that group management messages are not end-to-end encrypted or signed.

“When an administrator wishes to add a member to a group, it sends a message to the server identifying the group and the member to add. The server then checks that the user is authorized to administer that group, and (if so), it sends a message to every member of the group indicating that they should add that user. The flaw here is obvious: since the group management messages are not signed by the administrator, a malicious WhatsApp server can add any user it wants into the group. This means the privacy of your end-to-end encrypted group chat is only guaranteed if you actually trust the WhatsApp server.”

What now?
The main problem is this: end-to-end encryption, which WhatsApp purports to offer, should not depend on uncompromised servers. “We haven’t entirely achieved this yet, thanks to things like key servers. But we are making progress. This bug is a step back, and it’s one a sophisticated attacker potentially could exploit,” Green noted.

The researchers disclosed their findings to WatsApp last summer. WhatsApp said that the “group invitation bug” is a theoretical danger that’s additionally minimized by the fact that users will receive a notification about a new user joining the group. Also, the spokesperson noted, administrators could warn users about the new, unauthorized addition via private messages. That seems to be enough for them at the moment, especially because a fix for the flaw could end up breaking the convenient “group invite link” feature.

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