Hackers can apparently create malicious subtitle files that run code when they’re loaded into a media player, according to the report published by Check Point. The company estimates that hundreds of millions of users running software like VLC, Kodi, Popcorn Time, and Stremio could be at risk.
Subtitle files are generally perceived as being harmless, and as such they’re rarely vetted too stringently by media players or antivirus software. The situation is made worse by the fact that there’s little standardization, with over 25 different formats with different features and capabilities currently in use.
Check Point has also determined that subtitle repositories are being manipulated to help distribute the malicious files to users. Subtitles submitted by attackers are having are being boosted in the rankings, making it more likely that they’ll be downloaded by users, and selected by media players that can download such files automatically.
Having discovered these vulnerabilities, Check Point disclosed the problem to the developers responsible for the media players that were tested. Some had already taken steps to address the issues, while others are still looking into the situation. As of the time of writing, VLC and Stremio have been officially updated with a fix, while a fixed version of Popcorn Time is available here, and a fixed source code release of Kodi is available here. There are still concerns that other media players might also be affected.
The key here is that subtitle files are being exploited because they’re widely considered to be innocuous. As soon as users and developers drop their guard, malicious hackers see their window of opportunity — and that’s why the work done by organizations like Check Point is so important.