Determining the number of a Telegram user using brute force in the address book

Hello, friends. Today I will tell you about how you can try to find out the number of a person in the telegraph, knowing only his nickname.



Theory:



1. Add numbers to the phone’s address book up to the limit (if it ever exists in iOS or Android smartphones)

2. We look at the profile of the right person.

3. If his number is in the address book, this number will be displayed in the telegram profile

4. If not, continue to brutally add numbers to the bitter end



Regarding the first point - here you can write a script to automate actions, but since I do not know how to do this, I used my second phone to test the theory and it turned out to be working. I attach screenshots.

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Screen. №1 -

Screen. №2 -

Screen. Number 3 -

Screen. №4 -

I understand that this is not quite a bug, but rather a feature, to search for friends registered in the telegram, but there is no setting in the telegram to disable such a search for me by phone number (and display my number, in the profile, even if someone has my the number is in the address book) and, apparently, they don’t collect this setting, which is a direct security threat, because if an attacker finds out the phone number, he can intercept codes sent by SMS to log in to the account, or he can delete it if enabled additional password. How this has been done has been discussed more than once, both here and in HykTimes (through bribing employees of mobile phone shops, for example). And the lack of the ability to connect Google Authenticator instead of sms amazes me even more than what this topic is about.



I wrote about this issue at security@telegram.org 3 months ago, and in response there is still a complete silence.