Security Experts:

Telegram Leaks User IP Addresses

A vulnerability in Telegram Desktop results in the end-user public and private IP addresses being leaked during a call, a security researcher has discovered.

A cloud-based instant messaging and voice-over-IP service, Telegram was designed to provide users with secure communication capabilities, as messages are heavily encrypted and can self-destruct.

Tracked as CVE-2018-17780, the newly discovered issue affects Telegram Desktop (aka tdesktop) 1.3.14, and Telegram 3.3.0.0 WP8.1 on Windows, and is the result of a default, unsafe behavior where peer-to-peer (P2P) connections are accepted from clients outside of the My Contacts list.

Security researcher Dhiraj Mishra discovered that a default setting where Telegram clients used P2P connections while initiating a call could result in the user’s IP address being leaked.

Additional connection options are available in Settings > Privacy and security > Calls > peer-to-peer, but there was no option for setting “P2P > nobody” in tdesktop and Telegram for Windows, thus causing a privacy issue, the researcher says.

According to Mishra, a user’s IP address could leak on Telegram for Android as well, provided that the option hasn’t been set to “Settings > Privacy and security > Calls > peer-to-peer > nobody.” However, the Android client does provide the option.

To trigger the vulnerability in tdesktop, one would simply need to launch the application and initiate a call to another user, as the client would leak the IP address during call initialization.

The bug manifests itself even for incoming calls, with the recipient being able to view the public/private IP address of the caller in logs. The IP leaks even if the call is made from a Windows Phone.

“Not only the MTProto Mobile Protocol fails here in covering the IP address, rather such information can also be used for OSINT,” the researcher notes.

Telegram Desktop 1.3.17 beta and v1.4.0 are no longer impacted. The vulnerability has been addressed with the addition of an option for setting P2P to Nobody/My contacts. Mishra received a €2000 ($2300) bug bounty reward for the discovery.

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