Apple to fix Siri bug that exposed parts of encrypted emails

Apple may care about your privacy but that doesn’t mean it gets it right all the time, especially when it comes to training its Siri AI assistant. Last week, a researcher went public with a glaring security hole in the way that Siri gets to know you.

Apple IT specialist Bob Gendler was tinkering around in the macOS operating system to understand more about how Apple personalizes Siri for each user. During the process, he found that the operating system was storing portions of user emails in plaintext, even when they were supposed to be encrypted.

According to Gendler’s Medium post revealing the issue, Apple uses a system process called suggestd. Apple explains (as part of a help file system in the underlying BSD OS) that the program, which runs constantly, slurps content from various apps. These include Spotlight (the macOS indexing system), Mail, and Messages. It uses them to learn how you work and what you’re interested in, using it for things like news personalization.

When it read this information, it stores it in the snippets.db file inside the macOS Suggestions folder. Even emails encrypted with Secure/Multipurpose Internet Mail Extension (S/MIME), a technology that uses public and private keys to digitally sign and protect emails, didn’t escape. Suggestd stored the plaintext versions with no encryption at all in the database.

An attacker would need full disk access to your system files to look at this information, because macOS protects it with its System Integrity Protection feature, an OS X El Capitan-era security measure that ring fences important system files. However, we know from recent problems that some people have needed to turn this off, and Gendler says that any program with full disk access in macOS could potentially harvest the data. Because Apple’s Finder (the equivalent of Windows File Explorer) has full access, a rogue AppleScript program could do it.

What to do?

How do you stop macOS from storing your secret emails in plaintext? Simply turning off Siri won’t do it, because suggestd is still working behind the scenes. Instead, you can do it manually by entering a command in your terminal window (you don’t need to have root access to do it):

defaults write com.apple.suggestions SiriCanLearnFromAppBlacklist -array com.apple.mail