Tuta loads images from external resources

Summary

Tuta is an encrypted email service. In versions prior to 119.10, an attacker can attach an image in a html mail which is loaded from external resource in the default setting, which should prevent loading of external resources. When displaying emails containing external content, they should be loaded by default only after confirmation by the user. However, it could be recognized that certain embedded images (see PoC) are loaded, even though the "Automatic Reloading of Images" function is disabled by default. The reloading is also done unencrypted via HTTP and redirections are followed. This behavior is unexpected for the user, since the user assumes that external content will only be loaded after explicit manual confirmation. The loading of external content in e-mails represents a risk, because this makes the sender aware that the e-mail address is used, when the e-mail was read, which device is used and expose the user's IP address. Version 119.10 contains a patch for this issue.