Researchers Discover Flaw in Signal's Disappearing Messages Related to Mac Notification Center

by

Signal's Mac app displays recently received messages in the Notification Center on macOS, and this feature could compromise a user's disappearing private messages, as discovered by security researcher Alec Muffett and reported by Motherboard.

One of Signal's main advantages is its ability to send disappearing messages, so that after a predetermined amount of time the message is deleted from the app.

Muffett pointed out on Twitter this week that Signal's default Mac app settings somewhat defy this security measure due to the way Macs handle notifications. So, even if you send a self-destructing message within the Signal app, the messages remain on the recipient's Mac Notification Center, displaying your name and message details. Muffett was running macOS 10.13.4 and Signal version 1.9.0.


Mac security researcher Patrick Wardle then investigated the issue further, discovering that the "deleted" Signal messages that remain in the Notification Center are saved on the Mac's disk inside the operating system. While this is true of any app that displays notifications, it's particularly troublesome for Signal users in need of high-level security, like government workers or journalists.

Any malicious third parties would still need to get their hands on your Mac to get into your message history, so as Motherboard pointed out, "this is not a major threat for most people." Still, this could be a major security risk for high-level Signal users, since this means that any disappearing messages that popped up in Notification Center can be recovered later, "even after they are gone within the Signal app."

Wardle summed up his findings:

In short, anything that gets displayed as a notification (yes, including 'disappearing' Signal messages) in the macOS Notification Center, is recorded by the OS.

If the application wants the item to be removed from the Notification Center, it must ensure that the alert is dismissed by the user or programmatically! However, it is not clear that this also 'expunges' the notifications (and the their contents) from the notification database...i'm guessing not! If this is the case, Signal may have to avoid generating notifications (containing the message body) for disappearing messages...

Wardle said that Signal's iOS app does not appear to have a similar issue at this time, although the app "should be investigated." Of course, any Signal Mac user who is worried about potential privacy risks can navigate to Signal's Preferences menu on the top-left corner of the screen when the app is open, click Notifications, and "Disable notifications."

Tag: Signal

Top Rated Comments

(View all)
Avatar
29 months ago

Lol, right. I wouldn’t trust any of these supposedly secure messaging systems. Just because they haven’t discovered an exploit yet, doesn’t mean its not there and being exploited. Turning off features to patch of security holes after they’ve been made public isn’t going to do you much good at all.

Feel free to check the source code yourself then if you doubt it.
Score: 4 Votes (Like | Disagree)
Avatar
29 months ago
In short: Disable this feature, problem solved.
Score: 3 Votes (Like | Disagree)
Avatar
29 months ago

99.999% of the time, no point whatsoever.

Either the content is not worth encoding or it is being monitored by people more sophisticated in breaking the cypher than you are at encoding it. The "one time pad" is still the only unbreakable encryption method but, since it relies upon distributing multiple copies of the pad (to the sender and recipient(s)), it isn't secure either.

Well, sounds like there isn't a point to locks either since someone somewhere can certainly pick whatever one you might use.
Score: 1 Votes (Like | Disagree)
Avatar
29 months ago
This is ridiculous. You need to assume that anything you send to someone has been read and potentially recorded. These "disappearing messages" are misleading and anyone who takes them for temporary is simply naive.
Score: 1 Votes (Like | Disagree)
Avatar
29 months ago
I find it hilarious that someone can have the capacity and understanding of macOS to create a macOS app but somehow still doesn't understand that notifications are stored infinitely in Notification Center until the user manually clears them out. Hilarious but also annoying. Please Apple can we please please stop with the paper trails? I will never stop clearing (force quitting) my recent iOS apps and obsessively clearing Notification Center. They should auto-clear out after about an hour in my opinion. I don't care about the wallpaper I downloaded, decided I didn't like, and deleted a month ago. What is the point in showing me a notification from a month ago?

Edit: If you disable the notifications for an app they're just hidden but if you re-enable them in Sys Prefs all the old notifications come back. They don't go anywhere. How great is that :) :) :) :) :) :) :)
Score: 1 Votes (Like | Disagree)
Avatar
29 months ago
Honestly if you are getting a message that is compromising you likely don’t want t popping up as a banner on a larger screen than necessary anyway.
Score: 1 Votes (Like | Disagree)

Top Stories

8 Third-Party Home Screen Widgets That You Can Try Out Now on iOS 14

Wednesday August 5, 2020 12:56 pm PDT by
One of the biggest new features of iOS 14 is Home Screen widgets, which provide information from apps at a glance. The widgets can be pinned to the Home Screen in various spots and sizes, allowing for many different layouts. When the iOS 14 beta was first released in June, widgets were limited to Apple's own apps like Calendar and Weather, but several third-party developers have begun to test ...

Supposed iPhone 12 Display Unit Leaks

Thursday August 6, 2020 8:13 am PDT by
An image supposedly of an iPhone 12 display unit has been shared online by leaker "Twitter user Mr. White". Compared to images of an iPhone 11 Pro display piece, this new unit has a reoriented display connector, reaching up from the bottom of the display, rather than from the left-hand side on iPhone 11 Pro. This may be due to the logic board moving to the other side of the device. A...

Apple Seeds iOS 14 and iPadOS 14 Public Beta 4 to Testers

Thursday August 6, 2020 10:05 am PDT by
Apple today seeded new public betas of upcoming iOS 14 and iPadOS 14 updates to its public beta testing group. Today's software releases, which Apple labels as fourth betas to keep them in line with developer betas, are actually the third betas that Apple has provided and they come two weeks after the prior beta releases. Public beta testers who have signed up for Apple's beta testing...

Apple Announces New 27-Inch iMac With 10th-Gen Processors, Up to 128GB RAM, 1080p Webcam, True Tone, and More

Tuesday August 4, 2020 8:07 am PDT by
Apple today announced a new 27-inch iMac with faster 10th-generation Intel Core processor options, next-generation AMD graphics, up to 128GB of RAM, a higher-resolution 1080p front-facing FaceTime camera, a True Tone display with a nano-texture glass option, a T2 chip, higher fidelity speakers, studio-quality microphones, and more. A breakdown of the new 27-inch iMac's features and specs:10th...

Google's $349 Pixel 4a vs. Apple's $399 iPhone SE

Wednesday August 5, 2020 1:45 pm PDT by
Google this week launched its newest smartphone, the $349 Pixel 4a, a low-cost device that's designed to compete with other affordable devices like Apple's iPhone SE. We picked up one of the new Pixel 4a smartphones and thought we'd check it out to see how it measures up to the iPhone SE, given that the two devices have such similar price points. Subscribe to the MacRumors YouTube channel ...

Everything New in iOS 14 Beta 4: Apple TV Widget, Search Improvements, Exposure Notification API and More

Tuesday August 4, 2020 11:14 am PDT by
Apple today released the fourth developer betas of iOS and iPadOS 14 for testing purposes, tweaking and refining some of the features and design changes included in the update. Changes get smaller and less notable as the beta testing period goes on, but there are still some noteworthy new features in the fourth beta, which we've highlighted below. - Apple TV widget - There's a new Apple TV...

Samsung Launches Galaxy Note 20, Galaxy Z Fold 2, and Galaxy Buds to Compete With Apple's iPhones and AirPods Pro

Wednesday August 5, 2020 10:07 am PDT by
Samsung today held a virtual Galaxy Unpacked event where it unveiled its next-generation smartphones that will compete with Apple's 2020 iPhone lineup, set to come out in the fall. Samsung announced the launch of the Galaxy Note 20 and the Galaxy Note 20 Ultra, the two newest devices in the Note lineup, and, more notably, the Galaxy Z Fold 2, Samsung's latest foldable smartphone. The...

Alleged 'iPhone 12' Images Depict Circular Array of Magnets in Chassis

Wednesday August 5, 2020 4:39 am PDT by
New images shared on Weibo appear to show a circular array of magnets housed inside an "iPhone 12" chassis. The unverified images depict 36 individual magnets in a circular arrangement, suggesting they could be related to mounting or charging. EverythingApplePro, who shared the Weibo-originating images on Twitter, also posted an image of an alleged iPhone 12 case with a similar array of...

2020 iMac Benchmarks Surface Online [Updated]

Thursday August 6, 2020 7:16 am PDT by
Benchmarks from the new 2020 iMac have today been shared online by Mac Otakara. The Geekbench benchmarks are from the newly-released 27-inch iMac with 3.0GHz Intel Core i5 processor and Radeon Pro 5300 graphics, compared to multiple specs of the previous 2019 iMac. The lowest spec 27-inch i5 iMac from 2020 performs about 20 percent better in multicore than the lowest spec 27-inch i5...

Third-Party RAM for 27-inch iMac Still Far More Affordable Than Apple's Checkout Upgrade Options

Wednesday August 5, 2020 3:06 am PDT by
Apple yesterday announced a new 27-inch iMac with faster 10th-generation Intel Core processor options, next-generation AMD graphics, and up to a whopping 128GB of RAM. To max out the RAM at checkout, Apple charges an additional $2,600, which is like buying another whole iMac. Fortunately, the memory in the 27-inch iMac is user-replaceable thanks to the easily-accessible memory backdoor...