Every so often we see a flaw in iOS that can render an entire app unusable. In the past, these bugs have affected apps like Safari and Messages. A new bug in iOS 16, however, can completely lock you out of the Mail app with a single email that contains some weird text in the “from” field. Here are the details and how it impacts each mail service…
iOS 16 Mail app crash due to rogue text
The flaw was discovered by the folks at Equinux, which makes a VPN Tracker service for Mac and iPhone. The team discovered this bug in iOS 16 while analyzing spam emails.
We started seeing iOS mail problems for multiple people on our team: Mail was crashing immediately on launch.
It turns out the team had all received the same spam message. Looking at the raw source of the message didn’t immediately reveal any red flags – it was a pretty basic HTML email. However, a look at the mail headers showed that the spammers had done something unusual in the “from” field.
Usually, the “From” field in an inbound email looks like this:
- From: email@example.com.
But the maliciously crafted email has a “From” field that looks like this instead:
- From: “”@example.com.
What this means, according to Equinux, is that “anyone can send any iOS 16 user an email that can lock them out of their inbox.” They’ve created a form field on their website that you can use to test the flaw, which they are referring to as “Mailjack.”
Mailjack can impact the Mail app on any device running iOS 16 (the stable release), iOS 16.0.1 on the iPhone 14, and the latest iPadOS 16 betas, but there are some caveats. Some mail services, including Gmail, Outlook, and Hotmail rewrite inbound emails to prevent things like this from happening.
Additionally, Gmail and Yahoo block these maliciously crafted emails entirely. But one of the email services that doesn’t do anything to protect against these emails is iCloud Mail, Apple’s own first-party option. There are also a number of IMAP mail services that “do not correct or rewrite inbound mails.”
A simple way to test is to use your iCloud email account, but note that it may be marked as spam (you need to check your spam folder). Note that not all email providers will deliver the message as they might rewrite emails before delivering to the device.
The email could also get trapped in the “Spam” inbox. In this situation, the Mail app will crash every time you look at your spam inbox. This is better than if the email was to appear in your primary inbox, but emails are able to escape to the primary inbox pretty easily depending on the sender.
The solution to this problem, for now, is to delete the email from your account on a device that’s not running iOS 16 or via a different mail client:
As soon as you delete the email from your account using another device, different email client or on the web, Mail updates your inbox and stops crashing. Moving the email to a subfolder in an IMAP email account will also fix your inbox, but Mail will crash again if you navigate to that folder.
We’ve reached out to Apple for comment. For the time being, you can test the Mailjack flaw for yourself on the Equinux website or just check the GIF below. (I tested it and don’t recommend trying it, but that’s up to you.)
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