Published: June 2024

Author: Apple Security Research Team

In October 2023, Apple released a security update fixing a critical bug now tracked as CVE-2023-40416. This vulnerability could potentially reveal sensitive information stored in device memory just by processing a maliciously-crafted image file. Unless you’ve updated to recent versions of iOS, iPadOS, or macOS, your device may remain at risk.

In this article, we’ll break down how this bug worked, how attackers could exploit it, and—most importantly—how you can make sure your data stays safe. We’ll also touch on the technical details for the more curious readers.

What Is CVE-2023-40416?

CVE-2023-40416 is a memory disclosure vulnerability in Apple’s ImageIO library, which is used by countless apps to open and display images. Due to poor memory handling, certain image files could trick this library into exposing fragments of process memory. That means attackers could potentially see bits and pieces of private data loaded in your device’s memory—think passwords, emails, chat messages, and more.

iOS 16.7.2 and iPadOS 16.7.2

If your device is on an earlier version, update ASAP.
You can check Apple’s official advisory here:
https://support.apple.com/en-us/HT213981

How Did the Vulnerability Work?

At its core, this bug was about improper memory management while handling images. When you opened an image—for example, in Messages, Mail, Safari, or even the Files app—ImageIO could be tricked into accidentally copying extra data from process memory and including it in the image’s decoded output. This extra data could get sent back to an attacker if the app tries to parse or send the processed image back (for instance, as a thumbnail or preview).

Imagine this like opening a postcard with a smudge that, if viewed under a special light, reveals secrets written in invisible ink.

The Technical Details (Simplified)

Apple hasn’t shared all the low-level details (for obvious safety reasons), but reports suggest a classic out-of-bounds read vulnerability. When certain image formats (like specially crafted TIFF or PNG files) were loaded, the parser could read more bytes than intended. This unintended read might pull out random chunks of memory—a goldmine for attackers searching for secrets.

Pseudo-code illustration

// Vulnerable pattern (simplified)
// src: pointer to image data, len: size from file
void decode_image(char* src, size_t len) {
    char buffer[256];
    // Oops! 'len' could be > 256, buffer overflow or over-read!
    memcpy(buffer, src, len);
    // Data in 'buffer' might include extra memory if crafted maliciously
    process_image(buffer);
}

In this scenario, if an attacker crafts 'len' to be larger than the actual size of the image data, arbitrary memory beyond the expected image gets copied into 'buffer', and may be processed or displayed—revealing content to the attacker.

How Could Hackers Exploit CVE-2023-40416?

The attack vector is remote and user interaction is often minimal. All an attacker needs to do is get you to open a malicious image. This could happen via:

A shared file in iCloud Drive, AirDrop, or other file sharing

Once opened, the app would process the image using the vulnerable ImageIO library, and the attacker could extract leaked memory data (sometimes sent back as metadata, as part of a reply, or via an error report).

Exploit Example

Here’s a simple proof-of-concept in Python that simulates how an attacker might generate a malicious image (for a theoretical example only):

with open("leaker_image.png", "wb") as f:
    # Write a valid PNG header
    f.write(b'\x89PNG\r\n\x1a\n')
    # Write a chunk with incorrect length that causes over-read
    f.write(b'\x00\x00\x10\x00')  # Large chunk size
    f.write(b'IDAT')              # Chunk type
    # Fill chunk with minimal image data, rest will be process memory
    f.write(b'\x00' * 16)
    # The app may read beyond the image data when parsing (vulnerable case)
    f.write(b'IEND')

Note:
It’s not ethical or safe to attempt real-world exploitation. Wait for security experts and Apple to share sanitized demonstrations on how to recognize such attacks.

Any uninitialized memory is properly sanitized before use.

Reference:
Apple’s release notes –
Apple Security Updates

Beware Unexpected Images

Be cautious about images received from unknown contacts, especially those received via email, chat, or untrusted websites.

Final Thoughts

CVE-2023-40416 is a textbook example of how even basic image viewing can become a security risk in today’s world of complex operating systems and apps. One file, when processed by a vulnerable app, could leak pieces of your private life.

- CVE-2023-40416 at NIST
- Apple Security Releases
- Apple’s Advisory: HT213981

Timeline

Published on: 10/25/2023 19:15:09 UTC
Last modified on: 11/02/2023 13:42:32 UTC