macOS 'Quick Look' Bug Can Leak Encrypted Data Through Thumbnail Caches

A long-standing bug in macOS's Quick Look feature has the potential to expose sensitive user files like photo thumbnails and the text of documents, even on encrypted drives, according to security researchers.

Details on the Quick Look flaw were shared earlier this month by security researcher Wojciech Regula and over the weekend on security researcher Patrick Wardle's blog (via The Hacker News).

quicklookbug

Image via Wojciech Regula

Quick Look in macOS is a convenient Finder feature that's designed to present a zoomed-in view when you press the space bar on a photo or document that's selected.

To provide this preview functionality, Quick Look creates an unencrypted thumbnail database where thumbnails of files are kept, with the database storing file previews from a Mac's storage and any attached USB drives whenever a folder is opened. These thumbnails, which provide previews of content on an encrypted drive, can be accessed by someone with the technical know how and there's no automatic cache clearing that deletes them. As Regula explains:

It means that all photos that you have previewed using space (or Quicklook cached them independently) are stored in that directory as a miniature and its path. They stay there even if you delete these files or if you have previewed them in encrypted HDD or TrueCrypt/VeraCrypt container.

This is an issue that's existed for at least eight years and concerns have been raised about it in the past, but Apple has made no changes in macOS to address it. "The fact that behavior is still present in the latest version of macOS, and (though potentially having serious privacy implications), is not widely known by Mac users, warrants additional discussion," writes Wardle.

As Wardle points out, this information is valuable in law enforcement investigations, but most users are not going to be happy to learn that their Mac records file paths and thumbnails of documents from every storage device that's been attached to it.

For a forensics investigation or surveillance implant, this information could prove invaluable. Imagine having a historic record of the USB devices, files on the devices, and even thumbnails of the files...all stored persistently in an unencrypted database, long after the USB devices have been removed (and perhaps destroyed). For users, the question is: "Do you really want your Mac recording the file paths and 'previews' thumbnails of the files on any/all USB sticks that you've ever inserted into your Mac?" Me thinks not...

It's worth noting that if the main drive on the Mac is encrypted, the Quick Look cache that's created is too. Wardle says that data "may be safe" on a machine that's powered off, but on a Mac that's running, even if encrypted containers are unmounted, the caching feature can reveal their contents.

"In other words, the increased security encrypted containers were thought to provide, may be completely undermined by QuickLook," writes Wardle.

Wardle recommends that users concerned about unencrypted data storage clear the Quick Look cache manually whenever a container is unmounted, with instructions for this available on Wardle's website. It's also worth checking out Wardle's site for full details on the Quick Look bug.

Top Rated Comments

luvbug Avatar
34 months ago
It's a one line command (in terminal) to clear the cache. You need to be an "admin" user, but you don't need to be root:

qlmanage -r cache

Of course, someone here will figure out a reason to whine about having to do this.
Score: 20 Votes (Like | Disagree)
InuNacho Avatar
34 months ago
I’ve known about this for years. I accidently locked a word file and was able to “rescue” it by hitting the space bar.
Great security.
Score: 18 Votes (Like | Disagree)
magicschoolbus Avatar
34 months ago

This is an issue that's existed for at least eight years and concerns have been raised about it ('http://osxdaily.com/2010/07/25/filevault-and-quicklook-leak-some-information-from-encrypted-volumes/') in the past, but Apple has made no changes in macOS to address it. "The fact that behavior is still present in the latest version of macOS, and (though potentially having serious privacy implications), is not widely known by Mac users, warrants additional discussion," writes Wardle.

Apple does not care about the Mac. The hardware and this proves it. You guys should seriously consider naming this site iosrumors.com (that's not a shot at you either.. Apple is all about iOS)
Score: 17 Votes (Like | Disagree)
Acidsplat Avatar
34 months ago

So, you get the prize for first whiner! I guess assigning blame is more important to you than addressing the problem in the first person using readily available information.

Ordinary people wouldn’t know to input a terminal command, or even know that Quick Look is leaking their data.

The bug lies with Apple’s code. How is this the fault of the consumer? The consumer is certainly not the party to blame in this situation.
Score: 12 Votes (Like | Disagree)
Acidsplat Avatar
34 months ago

It's a one line command (in terminal) to clear the cache. You need to be an "admin" user, but you don't need to be root:

qlmanage -r cache

Of course, someone here will figure out a reason to whine about having to do this.

You shouldn't have to do this because of a bug in the software left in from literally years ago.
Score: 11 Votes (Like | Disagree)
AL1630 Avatar
34 months ago
Hmm. It seems like these flaws are becoming more common lately. Not sure if that's just me paying more attention or if the amount of flaws is actually increasing.
Score: 8 Votes (Like | Disagree)

Top Stories

16inchmacbookpromain

Kuo: New MacBook Pro Models to Feature Flat-Edged Design, MagSafe, No Touch Bar and More Ports

Thursday January 14, 2021 9:32 pm PST by
Apple is working on two new MacBook Pro models that will feature significant design changes, well-respected Apple analyst Ming-Chi Kuo said today in a note to investors that was obtained by MacRumors. According to Kuo, Apple is developing two models in 14 and 16-inch size options. The new MacBook Pro machines will feature a flat-edged design, which Kuo describes as "similar to the iPhone 12" ...
iphone x camera close

iOS 14.4 Will Introduce Warning on iPhones With Non-Genuine Cameras

Thursday January 14, 2021 8:07 am PST by
In the second beta of iOS 14.4 seeded to developers and public testers this week, MacRumors contributor Steve Moser has discovered code indicating that Apple will be introducing a new warning on iPhones that have had their camera repaired or replaced with aftermarket components rather than genuine Apple components. "Unable to verify this iPhone has a genuine Apple camera," the message will...
prototype iphone 12 pro

Prototype iPhone 12 Pro Shown Off in Photos

Wednesday January 13, 2021 3:39 pm PST by
Developer Giulio Zompetti, who often shows off prototype versions of Apple devices, today highlighted a prototype version of the iPhone 12 Pro. The iPhone 12 Pro is running an operating system called SwitchBoard, a nonUI version of the iOS 14 update that Apple uses internally. We've seen SwitchBoard on prototype devices before, as Apple uses it to test new features. Zompetti's prototype...
find my app safari post

Safari Allows Users to Enable Hidden 'Items' Tab in 'Find My' App Ahead of AirTags Launch

Wednesday January 13, 2021 5:45 am PST by
As seen in screenshots obtained by MacRumors in 2019, Apple's long-rumored AirTags items trackers are expected to be managed through the Find My app on iPhone, iPad, and Mac. Now, any user can get an early look at this tab. MacRumors reader David Chu today alerted us that the hidden "Items" tab in the Find My app can be enabled on an iPhone or iPad by typing in the link findmy://items in...
pioneer carplay wc5700nex

The Best Apple-Related Accessories at CES 2021

Wednesday January 13, 2021 1:16 pm PST by
CES 2021 is taking place digitally this year, and it hasn't been as exciting as in past years because many vendors have opted out. That said, some companies are still showing off some interesting Apple-related accessories that are coming out this year and that will be of interest to Mac, iPad, and iPhone users. Subscribe to the MacRumors YouTube channel for more videos. Pioneer Wireless...
Hue module dimmer switch

Philips Hue Announces New Wall Switch Module, Dimmer Switch, and Outdoor Light Bar

Thursday January 14, 2021 3:11 am PST by
Philips Hue has announced a new wireless dimmer switch module that lets Hue bridge owners directly control the smart lighting from their standard wall switches. The new Philips Hue wall switch module is the ideal addition to any Philips Hue set up. Installed behind existing light switches, it allows users to turn their existing switch into a smart switch and ensures their smart lighting is...
macbook pro 16 inch thunderbolt

Bloomberg: Next-Generation MacBook Pro to Offer Improved Displays, Faster Charging Over MagSafe

Thursday January 14, 2021 11:36 pm PST by
Following today's report from analyst Ming-Chi Kuo outlining major changes for the next-generation MacBook Pro models coming in the third quarter of this year, Bloomberg's Mark Gurman has weighed in with his own report corroborating some of the details but seemingly differing a bit on others. First, Gurman shares more details on the return of MagSafe charging to the MacBook Pro, indicating...
cook cbs this morning

CBS This Morning: Apple to Make 'Big Announcement' Tomorrow Morning

Tuesday January 12, 2021 8:46 am PST by
CBS This Morning today shared a short clip of an upcoming interview with Apple CEO Tim Cook in which addressing last week's events at the U.S. Capitol, with Cook saying "it's key that people be held accountable for it." Following the clip, Gayle King of CBS noted that the interview with Cook was not specifically arranged to address the current controversy over Parler and other repercussions, ...
iOS 14

Apple Seeds Second Betas of iOS 14.4 and iPadOS 14.4 to Developers [Update: Public Beta Available]

Wednesday January 13, 2021 10:03 am PST by
Apple today seeded the second betas of upcoming iOS 14.4 and iPadOS 14.4 updates to developers for testing purposes, with the new betas coming a month after Apple released the first betas. iOS 14.4 and iPadOS 14.4 can be downloaded through the Apple Developer Center or over the air after the proper profile has been installed on an iPhone or iPad. Paired with the HomePod 14.4 beta that is...
caldigit thunderbolt 4 dock featured

CalDigit Introduces USB-C Dock With 10 Ports and Up to 94W Charging for Macs [Updated]

Wednesday January 13, 2021 9:16 am PST by
CalDigit today unveiled a new Thunderbolt 4 dock with a wide selection of connectivity options, including three USB-A ports, one USB-C port, two HDMI 2.0 ports, a Gigabit Ethernet port, an SD card slot, and a 3.5mm headphone jack. The dock also has a Thunderbolt 4 port that allows it to be connected to a Mac with a single cable, with up to 94W of pass-through charging for the latest MacBook...