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macOS High Sierra more like 'Cry Sierra' for Mac-wielding beta testers

Early issues arise with new version of OS X 10.13

Apple's next version of the macOS, High Sierra, aka 10.13, is due for general release next week, and users running the beta have already noticed a pair of issues that could cloud the rollout.

The Cupertino phone flinger says that the Apple File System (APFS), a technology unveiled last year for the Mac, is going to cause some problems with Apple Fusion drives that will require anyone using the beta to revert their disks back to the old format.

The Fusion drives, offered in Mac Mini and iMac models sold from 2012 to 2017, marry solid-state and hard disk drive (HDD) hardware within a single enclosure. Apple said that while flash storage drives can be converted to APFS, hard disk and hybrid drives like the Fusion would not be – at least in the first builds.

Unfortunately, Apple said, the beta installations have already converted some versions that would no longer be supported when the beta program ends:

If you installed a beta version of macOS High Sierra, the Fusion Drive in your Mac may have been converted to Apple File System. Because this configuration is not supported in the initial release of macOS High Sierra, we recommend that you follow the steps below to revert back to the previous disk format.

Apple has posted a how-to guide for beta testers on reverting to the old macOS file system. The process will require an external hard drive and a Time Machine backup.

While annoying, the problem would fall squarely within the realm of risks users take when signing up to run public beta builds. Those who aren't using the beta builds, meanwhile, should not have much of a problem because the general release builds will not yet convert Fusion drives.

SKEL bypass

The second and potentially more serious issue is related to a key security feature being introduced in High Sierra. Researchers with security company Synack say that Secure Kernel Extension Loading (SKEL) – a feature Apple intended to use as a safeguard against rootkits and low-level malware infections – can be easily bypassed.

Designed to prevent malicious system extensions from obtaining kernel mode access, SKEL would block vulnerable kernel extensions from loading without user permission (given through the system preferences menu).

According to Synack chief researcher Patrick Wardle, however, SKEL doesn't do much to thwart bad actors. By using an undisclosed flaw in High Sierra, Wardle says he was able to simply sidestep the protections. In short, SKEL only works if the developer wants to let it work.

"Unfortunately when such 'security' features are introduced – even if done so with the noblest of intentions – they often just complicate the lives of 3rd-party developers and users without affecting the bad guys (who don't have to play 'by the rules')," Wardle explains.

"High Sierra's SKEL's flawed implementation is a perfect example of this."

Wardle told The Register that he disclosed the issue and his proof-of-concept to Apple, but he isn't optimistic that the fix will be out when High Sierra goes gold next week.

"They indicated that it likely would not be patched when High Sierra is released, meaning they're shipping a feature that hampers/hinders legitimate third-party security tools and software, yet is known to be trivial to bypass," he said.

"Of course, nobody really believes that SKEL's main priority is security ... it's all about Apple locking down the system (kernel) from third-party developers."

A summary of features new to High Sierra can be found here and here. This flavor of macOS will also be the last to support 32-bit apps on Macs. ®

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