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Apple fixes flaw that displayed actual password rather than password hint

If you’re running macOS High Sierra on your desktop or laptop, stop right now and make sure you have applied the latest security update.

Yesterday, Apple released a free supplemental update to macOS High Sierra 10.13 – just over one week since the general release of the operating system.

As an Apple support knowledgebase article explains, macOS High Sierra shipped with a potentially disastrous security hole in its Disk Utility tool that could have allowed anyone to access encrypted Apple File System (APFS) volumes.

As Brazilian developer Matheus Mariano discovered , a bug in the operating system’s code meant that clicking on the “Show Hint” button when attempting to access an encrypted volume would *not* display the password hint as you would expect.

Instead, it would display the actual plaintext password for the volume.

In short, if you don’t know the password don’t panic. Just hit the password hint button and the operating system will tell you.

Mariano demonstrated the security flaw in a YouTube video:

According to Apple, the password can be displayed instead of the password hint if you use Disk Utility to add an encrypted APFS Volume, and you supplied a password hint.

Fortunately, the new supplemental update patches macOS High Sierra 10.13 – as well as against other bugs, including a zero-day flaw that could allow a malicious attacker to steal passwords from the Keychain.

The update can be easily downloaded and applied using the Software Update functionality within the Mac App Store.

In its knowledgebase article, Apple recommends that after updating macOS High Sierra you go through a process to erase and recreate affected encrypted APFS volumes

To its credit, Apple issued a fix for the password-revealing bug very quickly, and its responsiveness in addressing this issue should be applauded. However, that doesn’t change the fact that such a serious bug like this really should have been intercepted during its quality control process, rather than allowed to ship to millions of computers around the world.

About the author

Graham CLULEY

Graham Cluley is an award-winning security blogger, researcher and public speaker. He has been working in the computer security industry since the early 1990s, having been employed by companies such as Sophos, McAfee and Dr Solomon's. He has given talks about computer security for some of the world's largest companies, worked with law enforcement agencies on investigations into hacking groups, and regularly appears on TV and radio explaining computer security threats.

Graham Cluley was inducted into the InfoSecurity Europe Hall of Fame in 2011, and was given an honorary mention in the "10 Greatest Britons in IT History" for his contribution as a leading authority in internet security.

5 Comments

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  • "According to Apple, the password can be displayed instead of the password hint if you Disk Utility to add an encrypted APFS Volume, and you supplied a password hint"… "if you Disk Utility" ????

  • Quality control? Don't make me laugh – they can't afford the time, with the pressure the marketing department are putting on them to get products out of the door and into the shops! Large organisations tend to make the least secure software, IMO.

  • The symptoms described suggest that there were two bugs rather than one. Let us hope that they fixed both.

    1) The password hint code is displaying the wrong information.
    2) Operating systems should not store passwords directly. They should instead store either a password hash or an encrypted key.

    Note that without the second bug the first could not have leaked the password.

  • The upgrade to APFS in High Sierra only affects Mac's with SSD drives. If you have a hybrid or physical hard drive you're still left running HPFS after the OS upgrade. An AFPS upgrade for non-SSD drives is expected some time in the future.