Google Shares Details on Unpatched 'High Severity' macOS Kernel Flaw

Google's Project Zero team in November found a "high severity" macOS kernel flaw that was recently disclosed (via Neowin) following the expiration of a 90 day disclosure deadline.

As explained by Google, the flaw allows an attacker to modify a user-owned mounted filesystem image without informing the virtual management subsystem of the changes, meaning a hacker can tweak a file system image without user knowledge.

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This copy-on-write behavior works not only with anonymous memory, but also with file mappings. This means that, after the destination process has started reading from the transferred memory area, memory pressure can cause the pages holding the transferred memory to be evicted from the page cache. Later, when the evicted pages are needed again, they can be reloaded from the backing filesystem.

This means that if an attacker can mutate an on-disk file without informing the virtual management subsystem, this is a security bug. MacOS permits normal users to mount filesystem images. When a mounted filesystem image is mutated directly (e.g. by calling pwrite() on the filesystem image), this information is not propagated into the mounted filesystem.

According to Google, Apple has not yet fixed this issue. Apple is planning to implement a fix in an upcoming software update, however.

We've been in contact with Apple regarding this issue, and at this point no fix is available. Apple are intending to resolve this issue in a future release, and we're working together to assess the options for a patch. We'll update this issue tracker entry once we have more details.

Google released the details on the bug without a fix from Apple because of its Project Zero policies. After discovering a security flaw, Project Zero provides details to the company that makes the software, providing them with 90 days to fix it before disclosure.

Google then publicly shares details on security flaws when a bug is fixed or when the 90-day deadline expires. Apple was informed of the bug in November, and the 90 day period elapsed without a fix.

Mac users should, as always, be wary of the files they're downloading to avoid attacks like this, making sure to download files only from trusted sites. It's not known if this is a bug that's easy to exploit, but Google has marked it as severe because it has the potential to bypass macOS safeguards.

Tag: Google

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Top Rated Comments

StellarVixen Avatar
70 months ago
It happens when you neglect things...
Score: 25 Votes (Like | Disagree)
5105973 Avatar
70 months ago
A teenager and Google trying to make Macs more secure :eek: and Apple's reported response to them looks like "talk to the hand". :confused:

What are they doing over in the spaceship? I'm not even remotely technically literate so I'm genuinely curious: is this a sign of internal mismanagement or nothing really of consequence but makes an interesting headline?
Score: 20 Votes (Like | Disagree)
quatermass Avatar
70 months ago
But, but, but... New Emojis! No really, look, over here - new emojis! And thinner too!
Score: 20 Votes (Like | Disagree)
arkitect Avatar
70 months ago
A teenager and Google trying to make Macs more secure :eek: and Apple's reported response to them looks like "talk to the hand". :confused:

What are they doing over in the spaceship? I'm not even remotely technically literate so I'm genuinely curious: is this a sign of internal mismanagement or nothing really of consequence but makes an interesting headline?
By the looks of it, running around in circles…
Score: 20 Votes (Like | Disagree)
eagle33199 Avatar
70 months ago
Out of curiosity, has Google's Project Zero disclosed unpatched issues in Google's own software? I've heard of a few directed at Apple products, but none directed at Google's own products...
Score: 13 Votes (Like | Disagree)
nate13 Avatar
70 months ago
I think the likelyhood of being exposed to this venerability is quite low (assuming they need physical possession of your hardware, to start). What brought me to the forum was to say, I'm glad for news like this. Not that venerabilities aren't bad, but because knowing there are teams identifying and resolving these issues is making a secure future for everyone. Sure, there are people who can flame Apple for not fixing sooner (I'm sure there are legitimate reasons, not some dude saying "nah, not today Google"), but that we have a culture that is pushing security is encouraging.

I'd be interested to know how many negative commenters are knowledgeable in low level kernel/ file system architecture to even reproduce the venerability, let alone patch it to an installed base of millions of users. It's so easy to critique things you don't understand.
Score: 12 Votes (Like | Disagree)