In July 2022, Apple patched a critical vulnerability known as CVE-2022-48503, impacting the famous WebKit browser engine. This subtle flaw allowed attackers to run malicious code simply by getting a user to visit a crafted website. The vulnerability was addressed in tvOS 15.6, watchOS 8.7, iOS 15.6 and iPadOS 15.6, macOS Monterey 12.5, and Safari 15.6. Let’s break down how the bug worked, what went wrong in WebKit’s code, and what an exploit could look like—all in plain English.

What Is WebKit?

WebKit is the “engine” that powers Apple’s Safari browser and web content on many other Apple apps. If you’re using an iPhone, iPad, Mac, Apple Watch, or Apple TV, WebKit is working in the background whenever you view web content.

Understanding Bounds Checking

Bounds checking makes sure programs don’t read or write outside the allowed area of memory. If a program skips these checks, bad stuff can happen: attackers can take control of your device.

In the case of CVE-2022-48503, a function in WebKit skipped a necessary bounds check while handling web content. This meant an attacker could trick WebKit into reading memory it wasn’t supposed to—or even writing to it.

Breaking Down the Patch

Though Apple doesn’t publish the exact source code of its vulnerabilities, we can reconstruct a simplified example of what might have gone wrong:

Buggy code (before the fix)

void handleInput(char *input, int length) {
    char buffer[100];
    memcpy(buffer, input, length); // No bounds check!
}

If length is longer than 100, memcpy writes outside the buffer.

Patched code (after the fix)

void handleInput(char *input, int length) {
    char buffer[100];
    if (length > 100) length = 100; // Now we check!
    memcpy(buffer, input, length);
}

This simple check makes sure memcpy never writes beyond the limits.

How Exploiting This Bug Works

Attackers make a malicious website containing web content that triggers the buggy part of WebKit. By controlling the input size (like the length above), they can force WebKit to overwrite memory. This lets them:

Execute arbitrary code (take over your device)

The last one—arbitrary code execution—is the scariest. Imagine visiting a shady site and, without any warning, your phone is compromised.

A Hypothetical Exploit

Below, let’s look at a very simplified JavaScript code snippet that could (hypothetically) demonstrate how an exploit might try to abuse such a bug:

// Hypothetical overflow trigger
let arr = new Array(100).fill('A');

for (let i = ; i < 100000; i++) {
  arr.push('B'); // Trying to overflow internal buffer
}

// Now try to read/write past the end
console.log(arr[100000]);


Remember: Modern browsers have many layers of defense, so just this code wouldn’t work on real Safari—but it suggests how an overflow might be triggered.

Once the attacker gets code execution, they could install spyware, steal your data, or manipulate your device to perform further attacks.

Fixes and Protections

Apple responded by improving bounds checks wherever they process web content. The issue was fixed in all major platform updates in July 2022.

Safari 15.6

Not sure if you’re safe? Update your device right away.

Original References

- Apple Security Updates — July 2022
- NVD Entry for CVE-2022-48503

Final Thoughts

CVE-2022-48503 was a dangerous bug that proved how small coding mistakes—like forgetting a bounds check—can put millions of Apple users at risk. Web browsers are complex and attackers are always looking for new ways in. That’s why it’s so important to keep your software updated and stay informed about security news.

Want to learn more about browser exploits?

Check out these resources

- Browser Security Handbook by Google
- WebKit Security Blog

Timeline

Published on: 08/14/2023 23:15:00 UTC
Last modified on: 08/19/2023 00:42:00 UTC