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Obscure Bug Could Disable the %p%s%s%s%s%n Wi-Fi on Your iPhone or iPad

9to5Mac reports on a Wi-Fi bug discovered by Carl Schou: if you join a Wi-Fi network named “%p%s%s%s%s%n” from an iPhone or iPad, it will break both Wi-Fi and AirDrop. Even worse, restarting the device won’t fix it. You’ll have to reset your network settings by going to Settings > General > Reset > Reset Network Settings.

The root cause seems to be Apple failing to sanitize Wi-Fi network names. Those characters preceded by percent signs are commonly used in programming to format variables into an output string. It’s likely that the name gets directly passed into Apple’s code, causing a process crash.

We haven’t seen reports of Wi-Fi networks with this name in the wild yet, but now that the word is out, you can bet that some merry pranksters will take advantage of it. To play it safe, avoid joining any Wi-Fi network with a percent sign in its name.

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Comments About Obscure Bug Could Disable the %p%s%s%s%s%n Wi-Fi on Your iPhone or iPad

Notable Replies

  1. Quoting from the original article: " … If you are somehow affected by this […] reset all network settings and start over. In Settings, go to General → Reset → Reset Network Settings. This resets all saved Wi-Fi networks on the iPhone (as well as other things like cellular settings and VPN access), thereby removing the knowledge of the malicious network name from its memory."

    I heard about this from a friend a few days ago, found the fix noted above and told him ‘Don’t Panic’. :slight_smile:

  2. That works, but unfortunately, it’s a really big hammer for a comparably small nail. It’s essentially an all or nothing approach. What I’d like to see on iOS is something more granular, like on macOS where I can remove individual entries from a list (as done in many other places in iOS) rather than just a single big nuke-it-all button that sets me back hours until I’ve re-entered all my critical networking prefs.

  3. If the problematic SSID is still in range, you can get its info and use the “Forget” button to remove its configuration. Of course, this won’t solve anything if the act of displaying the SSID breaks your networking.

    If you can somehow connect to a different SSID to reestablish networking, you can purge network settings from a Mac, which will be synced to your phone via iCloud Keychain.

  4. Unfortunately, there is a newly discovered one that cannot always be recovered with Reset Network Settings. For some people it takes a factory reset.

    I believe that I read that the iOS 15 beta is not affected by this/these bugs, so I’m hoping that Apple will be applying a permanent fix to the next release of iOS 14.

  5. I should hope so. A bug like this should be a 5-second fix followed by a well-deserved face-palm aimed at the developer who created it and everybody who supposedly reviewed the code.

  6. It’s the same as with purging data & history from Safari & DDGo. Unlike with Chrome & Firefox, where doing the data/cookies, history etc, purge allows open tabs & windows to remain, Safari kills all.

  7. There’s now another Wi-Fi network name that’s even a bit nastier. Hopefully, all this will go away shortly with the next iOS update.

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