A bug in siri reported by Brazilian site Mac Magazine allows anyone to request the virtual personal assistant read hidden messages aloud.
As of iOS 11, you can set message notifications to be hidden on your Lock screen – you can see that a message has arrived, but its content is hidden. That setting is on by default on the iPhone X, where simply glancing at it will unlock the phone and allow the content to be displayed, while it can be set on other models.
While Mac Magazine was testing the feature, which is on by default in the iPhone X, it discovered that requesting Siri read aloud whatever message had just come in would reveal the content of that message in nearly every case.
The one exception is Apple’s own Messages app, where Siri will read them only if the phone is unlocked. But for other messaging apps like WhatsApp, Telegram and Skype, Siri will happily disclose the content of the messages to anyone who picks up the locked phone.
According to 9to5Mac, The site verified that the bug is in both iOS 11.2.6 and the beta of iOS 11.3. It has reported it to Apple.
To hide or show message content on the Lock screen, go into Settings > Notifications, choose the app, select Previews and then choose your option.