In late 2022, security researchers and Apple disclosed a high-impact vulnerability affecting a huge range of Apple products. Registered as CVE-2022-42808, this flaw let remote attackers potentially execute code right inside the Apple kernel—the heart of every iPhone, iPad, Mac, Apple TV, and Apple Watch. Let’s break down what CVE-2022-42808 is, how it works, and how it was fixed, all in straightforward English.

What is CVE-2022-42808?

CVE-2022-42808 describes an out-of-bounds write vulnerability in the XNU kernel, Apple’s core system component. The flaw was reported by Apple itself and quickly patched in several updates:

watchOS 9.1

> Apple’s official blurb:
> “An out-of-bounds write issue was addressed with improved bounds checking. A remote user may be able to cause kernel code execution.”

This means, before the patch, malicious data could corrupt kernel memory and possibly run code at the highest privilege level, all without physical access.

Read the official Apple page:

- Apple security updates (CVE-2022-42808)
- Apple Security Release Notes - iOS 16.1

Out-of-Bounds Write: Explained Simply

An *out-of-bounds write* happens when a program tries to write data outside the memory space it’s allowed to use. Think of a row of mailboxes, each holding a letter for a specific person. If someone stuffs a letter in the wrong (non-existent) box, it could overwrite someone else’s mail or break the whole system.

The XNU kernel handles critical operations across all Apple products. If its memory is corrupted, attackers can hijack the device’s deepest workings.

Where Was the Bug?

The bug was reportedly in a function that handled user-supplied data buffers, but failed to properly check if the buffer size matched expectations. This allowed an attacker to write past the memory “edge,” potentially overwriting important data.

Here’s a simplified C code snipplet that demonstrates this type of flaw

// Simplified vulnerable kernel code
void vulnerable_copy(void* buffer, size_t user_size) {
    char kernel_buffer[256];
    // BAD: Not checking if user_size > kernel_buffer size
    memcpy(kernel_buffer, buffer, user_size);
}

What went wrong?
In this example, if user_size is bigger than 256, we’ll overwrite memory past kernel_buffer. In a real exploit, attackers carefully craft their input to overwrite sensitive kernel structures.

Send Malformed Data Remotely:

Since Apple’s advisory mentions “remote user,” imagine a situation where a network request, message, or shared file triggers the vulnerable kernel call.

Careful Buffer Overflow:

The attacker crafts data that sets user_size greater than expected. They fill the overflow with bytes designed to:

Simple Exploit Outline

# PoC: send oversized data to trigger out-of-bounds write.
payload = b"A" * 300  # 300 bytes, when kernel expects 256, overflows by 44 bytes.

# Let's imagine this gets sent to a vulnerable kernel service.
send_to_kernel(payload)

> Real-world exploits are much more complex, but the gist is the same: overstuff a buffer and take control.

The Patch: “Improved Bounds Checking”

Apple fixed this issue by properly validating the size before copying memory. Returning to our C example:

// Fixed code
void safe_copy(void* buffer, size_t user_size) {
    char kernel_buffer[256];
    if (user_size > sizeof(kernel_buffer)) {
        // Log error, refuse to process
        return;
    }
    memcpy(kernel_buffer, buffer, user_size);
}

Now, user input can never overflow the kernel buffer.

There are not many deep public writeups yet, but keep an eye on

- Project Zero
- Objective-See Blog

If you haven’t, make sure your device runs the fixed version

- iOS/iPadOS 16.1 or later

References

- Apple "About the security content of iOS 16.1"
- NVD – CVE-2022-42808
- GitHub XNU source (for advanced readers)
- Kernel Out Of Bounds Bugs Explained - Project Zero *(hypothetical, for learning)*

Conclusion

CVE-2022-42808 is a classic reminder that even the most polished systems like Apple's can slip up on old bugs like out-of-bounds writes. If you patched your device, you’re safe. But for researchers and enthusiasts, this bug offers a clean blueprint on how simple mistakes can lead to full system compromise—and why rigorous code review and timely updates are critical.

Timeline

Published on: 11/01/2022 20:15:00 UTC
Last modified on: 11/03/2022 03:54:00 UTC