Do you use Kodi, Popcorn Time, VLC or Stremio? Do you use subtitles while you watch? If so, then you need to update the platform as Check Point researchers revealed that not all subtitles are benign text files and hackers can remotely take control of any device running vulnerable software via malicious subtitles.
The attack is not in the wild, since Check Point developed the proof of concept attack vector; however, with news of the attack vector and an estimated 200 million video players and streaming apps running vulnerable software, attackers might jump on the malicious subtitle wagon to gain remote access to victims’ systems.
Check Point pointed out that Kodi has nearly 40 million visitors per month, VLC has over 170 million downloads and Popcorn Time likely also has millions of viewers. With all being vulnerable, researchers called the malicious subtitle attack “one of the most widespread, easily accessed and zero-resistance vulnerability reported in recent years.”
Subtitles are often treated as a trusted source, automatically downloading from third-party repositories. There are dozens of subtitle formats and numerous shared online repositories like OpenSubtitles.org. The repositories can be gamed, allowing attackers “to take complete control over the entire subtitle supply chain.”
After an attacker manipulates subtitle rankings, a subtitle with malicious code would have the highest rank and automatically be downloaded without any user interaction required or even a man-in-the-middle attack.
In different attack scenarios, instead of a video player or streamer automatically downloading the malicious subtitle file, a user can be tricked to visit a site using one of the vulnerable players or opting to download a tainted subtitle file to use with a video.
You can see Check Point’s proof of concept attack in the video below.
Check Point summarized the damage as:
By conducting attacks through subtitles, hackers can take complete control over any device running them. From this point on, the attacker can do whatever he wants with the victim’s machine, whether it is a PC, a smart TV, or a mobile device. The potential damage the attacker can inflict is endless, ranging anywhere from stealing sensitive information, installing ransomware, mass Denial of Service attacks, and much more.
The attack vector “relies heavily on the poor state of security in the way various media players process subtitle files and the large number of subtitle formats.” The researchers added, “Media players often need to parse together multiple subtitle formats to ensure coverage and provide a better user experience, with each media player using a different method. Like other, similar situations which involve fragmented software, this results in numerous distinct vulnerabilities.”
Check Point isn’t giving out too many technical details on how to pull off the attack, since the company believes there are similar flaws in other media players. However, Kodi, VLC, Popcorn Time and Stremio were all contacted and have issued fixes for the vulnerability.
After Kodi rolled out a fix, XBMC Foundation’s Project lead Martijn Kaijser urged Kodi users to install the newest version as “any previous Kodi version will not get any security patch.”