Researchers discovered another round of privacy challenges for Telegram, the messaging app founded by Russian tech entrepreneur brothers Nikolai and Pavel Durov.
Sony Mobile Communications consultant Ola Flisbäck found that the messaging app displayed metadata that allows attackers to determine who Telegram users are messaging.
Flisbäck was “surprised by the amount of metadata received” about contacts, he wrote on Github. The app's metadata can also be exploited by a third party command-line interface client, providing attackers with more data to determine who the user is interacting with on Telegram. Worse, the app's default setting does not require users to agree to be connected. “As long as an attacker know [stet] the phone number of the victim and add it to the Android contacts the victim will show up as a Telegram contact and the attacker will automatically subscribe to the victim's metadata,” Flisbäck wrote.
Earlier this month, security researcher The Grugq noted that there is no way to encrypt an existing session. “This is error prone,” he wrote. “Tools that allow for mistakes encourage operational errors. If it is possible, it will happen.”
Telegram replied to The Grugq on Twitter, with a link to the company's FAQs, noting that “You can control precisely who sees your last seen/online status.” Matthew Green, a cryptographer and professor at Johns Hopkins University, tweeted that Telegram's “UX is nice. The crypto is like being stabbed in the eye with a fork.”
In February, Zuk Avraham, CEO of Zimperium, a mobile security start-up, claimed on his company's blog that Telegram “is not protecting users any better than any other page or app that uses SSL.” After the Paris attacks this month, security researcher Scot A. Terban said ISIS operatives used Telegram to claim responsibility for the attacks. Flisbäck closed his post about Telegram on Github, “See you on Signal!” – a reference to the encrypted messaging competitor of Telegram.
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