I read flatkill.org and there is something that I found interesting since I am looking into securing apps with Apparmor.
Almost all popular applications on flathub come with filesystem=host, filesystem=home or device=all permissions, that is, write permissions to the user home directory (and more), this effectively means that all it takes to "escape the sandbox" is
echo download_and_execute_evil >> ~/.bashrc. That's it.
Since apps store configuration in hidden files in the home folder, and they store those files everywhere, it is very hard to sandbox apps so that they don't try to do anything funny with hidden files in the home folder. I tried sandboxing Atril with Apparmor and it tries to load a lot of hidden files of unrelated apps. How it is possible to sandbox apps if they touch each other's configuration files?
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