CVE-2022-26726 - How an App Could Capture Your Screen on macOS & How Apple Fixed It

In 2022, Apple patched a significant security vulnerability known as CVE-2022-26726, which allowed a malicious app to capture a user’s screen without proper permissions. This bug affected Mac computers running macOS Monterey, Big Sur, Catalina, as well as some Apple Watch devices. In this article, we’ll break down what went wrong, how it was fixed, and what you need to know if you’re a Mac user or developer.

What Is CVE-2022-26726?

CVE-2022-26726 is a screen capture vulnerability discovered in Apple’s operating systems. Simply put, because of this bug, a rogue app could slyly record whatever was visible on your desktop, violating privacy and potentially leading to sensitive information leaks.

Apple’s Official Summary

> “An app may be able to capture a user’s screen. This issue was addressed with improved checks.”

*(See Apple Security Updates for the original reference.)*

How Did the Exploit Work?

While Apple did not release in-depth technical details (to prevent abuse), security researchers and analysts have pieced together likely scenarios for exploitation based on how macOS handles screen recording permissions.

The Screen Capture API

In macOS, apps that want to take screenshots or record the screen must explicitly ask for permission from the user. This is enforced by the Screen Recording privacy settings introduced in macOS Catalina.

Here’s how a typical (well-behaved) Mac app asks for access

import AVFoundation

let displayID = CGMainDisplayID()
let stream = CGDisplayStream(dispatchQueueDisplay: displayID, ...)

if #available(macOS 10.15, *) {
    // Check for Screen Recording permission
    let hasPermission = AVCaptureDevice.authorizationStatus(for: .video)
    if hasPermission == .authorized {
        // Proceed to capture screen
    } else {
        // Prompt user for permission
    }
}

But, due to CVE-2022-26726, it was possible to bypass this permission check under certain circumstances. This could happen if the app used a combination of private APIs or system flaws to access the screen buffer directly, side-stepping the visible prompts and notifications to the user.

Possible Exploit Concept

Suppose an attacker creates a fake or malicious app. By exploiting the flaw, their app could hook into system services or abuse legacy APIs to capture screens in the background. You, as the user, wouldn’t see any requests or notices — all your activities could be monitored silently.

Proof-of-Concept (Simplified Example)

*Note: For educational purposes only! Do NOT use or distribute malicious code.*

Here’s a basic high-level pseudocode showing what an exploit might look like

// This code is for illustration and does NOT actually exploit the bug. 
// Real-world exploits would use deeper system calls not allowed in public APIs.

import AppKit

func captureScreen() {
    let image = CGDisplayCreateImage(CGMainDisplayID())
    // Save or process image...
}

captureScreen()

Before the patch, an attacker might find ways to run the above without any permission prompts by exploiting flaws in system permissions or using hidden APIs. After the patches, such unauthorized capture is prevented by robust permission enforcement.

Apple’s patch log says

> “This issue was addressed with improved checks.”

Under the hood, this means Apple strengthened the system’s background checks to always enforce user consent, no matter how an app tries to grab the screen. If the app does not have explicit permission, screen capture simply won’t work.

If you haven’t updated your Mac or Apple devices, do so immediately. Here’s what you need

- For macOS Catalina users: Get Security Update 2022-004
- For macOS Monterey: Upgrade to 12.4 or later (details here)

For Apple Watch: Update to watchOS 8.6

You can check for updates under System Preferences > Software Update.

Conclusion

CVE-2022-26726 was a privacy risk that could have let shady apps spy on your Mac’s screen. Thankfully, Apple patched it quickly with better checks for screen capture permissions. Always keep your devices updated, and regularly review what apps you’ve granted screen recording access at System Preferences > Security & Privacy > Privacy > Screen Recording.

Staying safe starts with knowledge — and the latest software updates.

*This post is original and compiled exclusively for this request, summarizing public technical information in an easy-to-understand format.*

Timeline

Published on: 05/26/2022 19:15:00 UTC
Last modified on: 06/07/2022 22:43:00 UTC