The vulnerability affected Telegram versions 10.14.4 and older.
ESET researchers discovered the flaw after a proof-of-concept demonstration was shared on a public Telegram channel, allowing them to analyze the malicious payload. They confirmed that the exploit worked on Telegram v10.14.4 and older, naming it ‘EvilVideo.’ The vulnerability was responsibly disclosed to Telegram by ESET researcher Lukas Stefanko on June 26 and again on July 4, 2024.
Telegram responded on July 4, indicating that they were investigating the report.
Subsequently, they patched the vulnerability in version 10.14.5, released on July 11, 2024. This timeline suggests that threat actors had at least five weeks to exploit the zero-day vulnerability before it was patched.
While it remains unclear if the flaw was actively exploited in attacks, ESET shared a command and control server (C2) used by the payloads at ‘infinityhackscharan.ddns[.]net.’ BleepingComputer identified two malicious APK files using that C2 on VirusTotal that masqueraded as Avast Antivirus and an ‘xHamster Premium Mod.’
The EvilVideo zero-day exploit specifically targeted Telegram for Android. It allowed attackers to create specially crafted APK files that, when sent to other users on Telegram, appeared as embedded videos. ESET believes the exploit used the Telegram API to programmatically create a message showing a 30-second video preview.
The channel participants received the payload on their devices once they opened the conversation.
For users who had disabled the auto-download feature, a single tap on the video preview was enough to initiate the file download.
When users attempted to play the fake video, Telegram suggested using an external player, which could lead recipients to tap the “Open” button, executing the payload.
Despite the threat actor’s claim that the exploit was “one-click,” the multiple clicks, steps, and specific settings required for a successful attack significantly reduced the risk. ESET tested the exploit on Telegram’s web client and Telegram Desktop and found that it didn’t work on these platforms, as the payload was treated as an MP4 video file.
Telegram’s fix in version 10.14.5 now correctly displays the APK file in the preview, preventing recipients from being deceived by files masquerading as videos. Users who recently received video files requesting an external app to play via Telegram are advised to perform a filesystem scan using a mobile security suite to locate and remove any malicious payloads.
