Pierluigi Paganini April 20, 2019

A white hat hacker discovered how to break Tchap, a new secure messaging app launched by the French government for officials and politicians.

The popular French white hat hacker Robert Baptiste (aka @fs0c131y) discovered how to break into Tchap, a new secure messaging app launched by the French government for encrypted communications between officials and politicians.
The app was developed by DINSIC (Interministerial Directorate of Digital and Information System and Communication of the State), as a project controlled by France’s National Cybersecurity Agency (ANSSI).

It aims at replacing popular instant messaging services like Telegram and WhatsApp for government people.

The Tchap was launched on April 18 and is available on the official iOS and Android app stores, but only French government employees (using
@gouv.fr or @elysee.fr email accounts) can sign-up for an account.

The key point Tchap is that encrypted communications flow through internal servers to prevent cyber attacks carried out by foreign nation-state actors.

Anyway, the French government published Tchap’s source code on GitHub, it is based on Riot, a well-known open-source instant messaging client-server package.

News of the day is that Robert Baptiste found a security bug that could allow anyone to sign up an account with the Tchap app and access groups and channels without using an official government email account.

The expert made a dynamic analysis of the mobile app and discovered it implements certificate pinning in the authentication process. Even if he disables it with Frida, during the registration process, the app requests a token.

The expert noticed that depending on the email address provided by the user, the app will refer the “correct” id_server. The list of available servers is defined in the AndroidManifest.xml.

“I set id_server to matrix.agent.elysee.tchap.gouv.fr. For info, Elysée is the French presidential palace. As I choose this server I guessed I should have an @elysee.fr email address. So, in the requestToken request, I modified email to [email protected]@elysee.fr. Hum, no validation email in my inbox… Wait, maybe it is waiting a known @elysee.fr email address. So I did a Google search “email @elysee.fr”” wrote the expert in a blog post.

“So I did another try and in the requestToken request and I modified email to [email protected]@[email protected]. Bingo! I received an email from Tchap, I was able to validate my account! “

The expert demonstrated how to create an account with the service using a regular email ID by exploiting a potential email validation vulnerability in the Android version of the Tchap app.

After he logged as an Elysée employee, he was able to access to the public rooms.

Robert reported the issue the Matrix team who developed the Riot client, and it quickly fixed the bug and released a patch. The released patch was specific only to the application developed by French intelligence.

Just for curiosity, last week Matrix.org warned users of a security breach, a hacker gained unauthorized access to the production databases, including unencrypted message data, access tokens, and also password hashes.

According to Matrix.org, the attacker has exploited a known vulnerability in the Jenkins open source automation server to hijack credentials and gain access to the systems of the organization. Homeservers, source code and packages, identity servers, and Modular.im servers were not impacted.

Pierluigi Paganini

(SecurityAffairs – hacking, Tchap app)

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