Cybersecurity experts discovered a zero-day vulnerability in the Telegram messenger that allowed attackers to send malicious APK files disguised as video files. The vulnerability affected Android users and was successfully exploited to spread malware.
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According to the resource BleepingComputer, on June 6, on the XSS hacker forum, an attacker under the nickname Ancryno put up for sale a zero-day exploit (a method based on an attack with previously unidentified software vulnerabilities) for the Telegram messenger. The vulnerability, dubbed “EvilVideo,” was discovered by ESET and affected versions of the application up to 10.14.4 for Android users.
The attackers created special APK files that, when sent via Telegram, appeared as embedded videos. When trying to play such a video, Telegram suggested using an external player, which could prompt the victim to click the “Open” button, thereby running the malicious code.
ESET tested the exploit and confirmed its functionality. On June 26 and July 4, company specialists reported the problem to Telegram management. In response, on July 11, Telegram released version 10.14.5 of its application, which fixed the vulnerability. Although a successful attack required several actions on the part of the victim, hackers had at least five weeks to exploit the vulnerability before releasing a patch.
Interestingly, despite hackers’ “one-click” claim, the actual process requires several steps, reducing the risk of a successful attack. ESET also tested the exploit on Telegram Desktop, but it did not work there because the malicious file was treated as an MP4 video rather than an APK file.
The fix in version 10.14.5 now correctly displays APK files in the preview, eliminating the possibility of deceiving recipients. ESET recommends that users who have recently received videos asking you to open them using an external app should scan their file system using mobile antivirus software to find and remove malicious files.
As a reminder, Telegram files are usually stored in “/storage/emulated/0/Telegram/Telegram Video/” (internal storage) or “/storage//Telegram/Telegram Video/” (external storage).