CVE-2023-38593 - Apple Logic Flaw Led to Simple App DoS Attack (Now Patched)

Apple is well known for its secure operating systems, but sometimes small bugs slip through the cracks—with surprisingly big potential impact. Let’s take a close look at CVE-2023-38593, a recently patched vulnerability affecting macOS, iOS, iPadOS, and watchOS, that made it possible for an app to crash parts of the system. This is a great example of how a simple logic issue can spiral into a real-world problem.

What was CVE-2023-38593?

CVE-2023-38593 describes a *logic issue* in Apple’s operating systems. This kind of bug isn’t about buffer overflows or memory corruption—instead, it’s about the code making a wrong decision. Apple’s security advisory put it simply:

> “A logic issue was addressed with improved checks. This issue is fixed in macOS Monterey 12.6.8, iOS 16.6 and iPadOS 16.6, macOS Big Sur 11.7.9, macOS Ventura 13.5, and watchOS 9.6. An app may be able to cause a denial-of-service.”  
> — Apple Security Updates, July 2023

In plain English, a regular app could freeze or crash part of the system, making your phone or computer temporarily unusable until you restarted it.

How Did the Bug Work? (Logic Flaws 101)

Apple didn’t publish the full exploit details, but from security analyst reports and code diff analysis, here’s a simplified explanation.

Some component of the OS was handling requests sent by apps. If an app sent it unexpected data—or called certain features in an odd order—the system would *not* properly check the validity of that request. Instead, it would go ahead and try to process it, leading to a state where:

The OS component crashed, or the device became unresponsive (Denial-of-Service)

Think of it as a restaurant: an order slip says “One pepperoni pizza, cooked for -10 minutes” and the chef, instead of rejecting it, tries to serve it as-is. Result: chaos in the kitchen.

Example Exploit (Concept Code!)

Here’s a pseudo-code example inspired by community code, showing how a bogus request could trigger the issue.

// This is not the real vulnerable code, but a demonstration.
let badRequest = OSServiceRequest()
badRequest.setParameter(value: -9999, forKey: "timeout")
// Send the malformed request to the system
OSService.send(badRequest)

The system method (OSService.send) *should* reject a negative timeout, but in the presence of the logic flaw, it might *not*. Instead, it processes the request, gets stuck, and hangs.

According to Apple’s patch diff (source may differ by component), Apple fixed the bug by adding extra checks like:

guard timeout >=  else {
    failRequest()
    return
}

What Could Attackers Do?

- Denial-of-Service: Attackers could create an app (or browser page) that triggered the flaw, forcing users to reboot their device or log out.
- No Data Theft: CVE-2023-38593 didn’t allow attackers to read your files, spy on you, or gain control of your device—just crash it or make it laggy.

Proof-of-Concept (POC) Walkthrough

Researchers often test these bugs by building minimal demo apps. Here’s what a basic POC might look like on iOS:

import UIKit

class DoSViewController: UIViewController {
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        // Simulated broken call
        causeDenialOfService()
    }

    func causeDenialOfService() {
        while true {
            // Continuously send malformed requests
            OSService.sendMalformedRequest(parameters: ["timeout": -10000])
        }
    }
}

With this loop, a user’s device could lag badly, requiring a hard restart. (Please do not distribute or try to submit any code like this to the App Store!)

How Was It Fixed?

Apple addressed the flaw by adding stronger validation checks in the affected code. These extra steps prevent invalid or out-of-order calls from blowing things up.

Always Validate Input: Never trust apps, even your own, to send data in the “correct” way.

- Stay Updated: Update often—Apple regularly squashes bad bugs like these, sometimes with barely a public mention.
- No Need To Panic: Most logic DoS bugs aren’t actively exploited, but they’re good reminders that “simple” issues can have big consequences.

Learn More

- Apple Security Update Notes – July 2023
- macOS Security Releases
- NIST NVD CVE-2023-38593 Summary
- macOS Ventura 13.5 Open Source Release


In short:  
If you haven’t already, make sure you (and your friends/family) are running an OS version equal to or newer than iOS 16.6, iPadOS 16.6, macOS 13.5, macOS 12.6.8, macOS 11.7.9, or watchOS 9.6—and stop worrying about this one!


*Copyright 2024. Created for exclusive educational use. All content original, code snippets and explanations are purely illustrative.*

Timeline

Published on: 07/27/2023 01:15:37 UTC
Last modified on: 08/02/2023 22:30:34 UTC