WhatsApp Messages Can Be Intercepted, Manipulated

BLACK HAT USA 2019 – Las Vegas – Researchers from Check Point Software Technologies are once again warning about what they describe as a dangerous security weakness in the WhatsApp messaging application that can be abused to spread fake news and carry out various online scams.

In a technical presentation here yesterday, Check Point researchers Roman Zaikin and Oded Vanunu explained how an attacker could exploit the issue to alter the text of someone else's reply, change the identity of a message sender, or trick a user into sharing something publicly in a group that they might not have intended to share.

The researchers first surfaced the same issues in August 2018 in a report that described how attackers could intercept and manipulate WhatsApp messages in private and group chat settings. In a blog and in comments at the time to Dark Reading, Vanunu identified the issue as having to do with WhatsApp's failure to validate certain message parameters before encrypting and sending messages to the intended recipient.

Since then, Facebook-owned WhatsApp has fixed the issue that allowed attackers to trick users in a group chat into thinking they were sharing something in private when, in fact, it was visible to everyone else, he said.

However, the other two issues remain unmitigated and continue to give attackers a way to abuse WhatsApp in dangerous ways, Vanunu said. From Check Point's perspective, the vulnerabilities present a major threat and need to be addressed urgently, he noted.

"WhatsApp is not just an application. It is an infrastructure of more than 1.5 billion users with more than 56 billion messages per day," Vanunu said.  

WhatsApp's massive footprint makes it a big target for criminals attempting to spread fake news and carry out other malicious activities, he said. In some countries, including India and Brazil, rumors spread via WhatsApp have even resulted in the deaths of innocent people, Vanunu said.  In many countries, WhatsApp is also used for business application, so it is important that the issue gets resolved, he added.

According to Vanunu and Zaikin, WhatsApp's end-to-end encryption is strong and not the problem. Rather, the issue lies in the communication that happens between an individual's WhatsApp mobile app and its Web version when a user logs in.

Vanunu and Zaikin reverse-engineered the communication and identified several message parameters being exchanged between WhatsApp's mobile version and Web version. Among them were parameters pertaining to the content of the message, and those that identified the message sender and the contact or the group to which the message was intended.

The researchers found they could intercept the communication and manipulate the data associated with each parameter before any of it was encrypted. For instance, an attacker could use the "quote" feature in WhatsApp that references a previous message to change the identity of the original sender or alter the original message entirely. WhatsApp does not validate the data and instead just accepts the altered content, encrypts it, and forwards it to the intended recipient.

WhatsApp did not respond to a request for comment. But in a statement responding to Check Point's original report last year, the company denied any security issue. It likened the issue to someone altering the contents of an email to put words into the mouth of the sender.

A lot of it also has to do with how WhatsApp works. WhatsApp has noted that when someone replies to a message, the WhatsApp client copies the text available within the app and creates a kind of graphical representation that helps people follow the conversation. The reason for providing a sort of "quick reply" option is to help identify the source within the user's chat log if one exists.

WhatsApp has stressed that with its end-to-encryption, it does not store any messages on its own servers and therefore has no single reference point of any messages that is off the device itself. As a result, the only way to validate any data in messages being sent would be to log all messages, which would undermine privacy protections. It would also make it impossible to deliver messages to groups when a single person is not connected to it and undermine the ability for users to quote a message prior to a new group member, WhatApp said.

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