Security and privacy-focused, end-to-end encrypted messaging app Telegram has been found leaking both users’ private and public IP addresses by default during voice calls. To improve voice quality, Telegram by default uses a P2P framework for establishing a direct connection between the two users while initiating a voice call, exposing the IP addresses of the two participants. The company patched the issue in both 1.3.17 beta and 1.4.0 versions of Telegram for Desktop by setting your “P2P to Nobody/My Contacts”
Source: https://thehackernews.com/2018/09/hack-telegram-messenger.html