Black Hat 2019 – WhatsApp Protocol Decryption for Chat Manipulation and More

According to sources, WhatsApp, the Facebook-owned messaging application has over 1.5 billion users in over 180 countries. The average user checks WhatsApp more than 23 times per day. And, the number of WhatsApp users in USA is predicted to grow to 25.6 million by 2021.

Given all the chatter, the potential for online scams, rumors and fake news is huge. Threat actors have an additional weapon in their arsenal to leverage the messaging platform for their malicious intentions.

Towards the end of 2018, Check Point Research notified WhatsApp about new vulnerabilities in the popular messaging application that would enable threat actors to intercept and manipulate messages sent in both private and group conversations, giving attackers the power to create and spread misinformation from what appear to be trusted sources.

The Check Point Research team observed three possible methods of attack exploiting this vulnerability – all of which involve social engineering tactics to fool end-users. A threat actor may:

Use the ‘quote’ feature in a group conversation to change the identity of the sender, even if that person is not a member of the group.

Alter the text of someone else’s reply, essentially putting words in their mouth.

Send a private message to another group participant that is disguised as a public message for all, so when the targeted individual responds, it is visible to everyone in the conversation.

WhatsApp fixed the 3rd vulnerability which enabled threat actors to send a private message to another group participant disguised as a public message for all. But, we found that it is still possible to manipulate quoted messages and spread misinformation from what appear to be trusted sources.

Following the process of Responsible Disclosure, Check Point Research informed WhatsApp of its findings. From Check Point Research’s perspective, we believe these vulnerabilities to be of the utmost importance and require attention.

To demonstrate the severity of this vulnerability in WhatsApp, we created a tool that allows us to decrypt WhatsApp communication and spoof the messages.

As is well-known, WhatsApp encrypts every message, picture, call, video or any other type of content you send so that only the recipient can see it. WhatsApp does not have the ability to view these messages.

These encryption processes caught our attention, and we decided to try to reverse the WhatsApp’s algorithm to decrypt the data. Indeed, after decrypting the WhatsApp communication, we found that WhatsApp is using the “protobuf2 protocol” to do so.

By converting this protobuf2 data to Json we were able to see the actual parameters that are sent and manipulate them in order to check WhatsApp’s security.

The outcome of our research is a Burp Suit Extension and 3 Manipulation methods (the 3rd one was fixed our we disclosure the vulnerability to WhatsApp).

To start the manipulation, though, we first have to get the private and public key of our session and fill it in our burpsuit extension.