Newly Discovered Malware Targets Telegram Desktop

A new form of malware has emerged targeting the desktop version of end-to-end encrypted instant messaging service Telegram.

Cisco Talos researchers attribute the malware to a Russian-speaking attacker "with high confidence" and say it's mostly targeting Russian-speaking victims. They also found it's intentionally avoiding IP addresses related to anonymizer services.

What stands out about the malware is not that it affects Telegram Desktop - it's that it only affects Telegram Desktop, says Cisco Talos threat researcher Vitor Ventura. This is the first threat Talos has detected with the intent of hijacking Telegram Desktop sessions.

"There are other information stealers in the wild," he explains. "But this one, although it searches for other types of credentials, has a special focus on Telegram Desktop. We think it's important to point out the fact that Telegram Desktop is not secure by default. And this is what the malware authors are taking advantage of."

The malware doesn't exploit a vulnerability in the Telegram service, researchers explain. Instead it abuses weak default settings and lack of Secret Chat support in Telegram Desktop. An attacker can access conversations between desktop and mobile users if the desktop user is infected with this malware; however, mobile-to-mobile conversations are protected.

Mobile-only Secret Chats have guaranteed security because they are bound to the device, locally stored, and equipped with self-destruction tools. These features aren't on the desktop or Web versions, which store chats in the cloud and don't enable auto-logout by default.

The combination of cloud-based storage, and lack of auto-logout by default, enable this malware to hijack Telegram sessions and conversations.

When, What, Who

A first version of this malware was detected on April 4, 2018 stealing browser credentials, cookies, and all text files it can locate on the system. A second variant, spotted on April 10, added the ability to gather Telegram desktop cache, key files, and Steam website credentials. It's unusual to see attackers take Telegram Desktop data to hijack sessions, Ventura says.

"This data allows an attacker to be able to access all contacts and previous chats as long as the owner doesn't log out," he continues. "This is a privacy issue [and] accessing Telegram Desktop data is all about privacy and accessing confidential information."

The malware's operators use hardcoded pcloud.com accounts to store the information they take from Telegram. Because this data is not encrypted, anyone with access to the authors' account credentials will have access to the stolen information.

Why snatch this type of data? While he doesn't know the specific motivation, Ventura explains how he and his colleague, Azim Khodjibaev, determined its Russian attribution. An analysis of the malware linked it to a user who goes by the name of Raccoon Hacker.

The two researchers combined Talos intelligence with online videos to pinpoint the malware's author, who posted several YouTube clips containing instructions on how to use files collected from Telegram to hijack targets' ongoing sessions and package them for distribution. If a chat session is open, attackers can access the conversation, contacts, and previous chats.

A Need for Transparency

Ventura points out an opportunity to better inform Telegram users of the desktop version's shortcomings. During the installation process and start-up, he says, it's never mentioned that chats are not as secure as they are on mobile, or that Secret Chats are not available. Telegram also doesn't specify its default setting doesn't allow sessions to expire.

"It's understandable that an application prioritizes usability over security, but not acceptable in an application that claims to be a secure messaging platform," he says.