CVE-2023-23519 - Apple ImageIO Memory Corruption Vulnerability Explained
Apple is known for building secure devices. But even giants have cracks in their armor. In early 2023, Apple patched a serious memory corruption vulnerability in ImageIO (CVE-2023-23519) that could let a simple picture crash your iPhone, Mac, iPad, Apple Watch, or Apple TV. Let’s break down what this CVE is, how it works, what Apple fixed, and how you could exploit it, just for learning purposes.
Impact: Processing a malicious image can cause denial-of-service (DoS)
- Affected Platforms: macOS Ventura, iOS/iPadOS, tvOS, watchOS (pre-2023.2)
macOS Ventura 13.2
- iOS/iPadOS 16.3
watchOS 9.3
Read Apple’s own advisory here:
Apple Security Updates – January 23, 2023
The bug is listed at NVD: CVE-2023-23519.
Why Does This Matter?
ImageIO is used everywhere images appear on Apple devices: Safari, Messages, Previews, even many third-party apps. This means if you receive a specially crafted image – from a web page, text, or email – just looking at it could crash your app or device.
That’s a pretty big deal. Even though this bug “only” lets attackers lock you out with a crash (DoS), memory bugs can sometimes be turned into more serious attacks like code execution.
There aren’t public code details, but Apple said
> “A memory corruption issue was addressed with improved state management.”
Let’s decode that: ImageIO was tracking its work on images incorrectly. Under certain circumstances, the way it stored or handled image data could break the code’s expectations, causing it to access or overwrite memory it shouldn’t.
Simulating The Exploit: How Could This Bug Be Used?
To better understand, let’s look at how a crash-by-file bug might appear. Imagine ImageIO has a function like this (in simplified pseudo-C):
void processImage(ImageData* img) {
for (int i = ; i < img->numTiles; i++) {
processTile(img->tiles[i]);
}
}
If the file tricks ImageIO into thinking there are 1,000,000 tiles, but only provides 10, memory outside the valid range gets accessed. Classic out-of-bounds access.
Or maybe
unsigned char *buffer = malloc(img->size);
memcpy(buffer, img->data, img->size); // img->size is attacker-controlled here
If img->size is corrupted by malicious file data, it could cause malloc or memcpy to fail, crash, or corrupt memory.
A classic trick: Set a length or pointer field in a file header to a huge number, or a negative/zero number, and see what breaks when ImageIO tries to use it.
Quick Demo: Causing a Crash With a Malformed PNG
While we don’t have a proof-of-concept (Apple didn’t release one), here’s how crash files are often made:
2. Open a valid PNG
#### 3. Corrupt a chunk length or type field (for example, set an IDAT chunk length to zero or a huge value)
4. Save and try to open it on a vulnerable device
That’s it! If you have a pre-13.2 Mac or pre-16.3 iPhone, uploading or simply previewing such files could freeze the app or device.
A Python illustration of generating a broken PNG
with open('original.png', 'rb') as f:
data = f.read()
# For this example, let's say the IDAT chunk starts at byte offset 33
corrupt = bytearray(data)
# Set the length of the IDAT chunk to a giant value (e.g., xFFFFFFFF)
corrupt[33:37] = b'\xFF\xFF\xFF\xFF'
with open('crash.png', 'wb') as f:
f.write(corrupt)
NOTE: Do not send crash files to others. Only test on your own device and at your own risk.
How Did Apple Fix It?
Apple said they improved “state management.” Most likely, they added extra checks to make sure lengths, pointers, and counters don’t go out of bounds, and that files can’t claim impossible data.
This prevents attackers from using corrupted or malformed images to crash the system.
Web Attack: You browse a page with a crafted image – Safari or another browser crashes.
- Message/E-mail Attack: Attacker sends you a booby-trapped PNG – your Messages or Mail app freezes or quits.
Photos App: Importing a malicious image bricks the app or, in rare cases, the device.
Luckily, this flaw does not allow code execution. But it’s still a headache, especially if a legit photo goes viral and causes chaos for unpatched devices in the wild.
What Should You Do?
Update your Apple devices!
watchOS: 9.3+
Go to _Settings → General → Software Update_ and install any available updates.
References
- Apple Security Updates
- NIST NVD Entry (CVE-2023-23519)
- Apple About ImageIO
- PNG File Structure
If you're interested in security, studying this kind of bug is a great way to understand the hidden dangers in code you use daily!
Final Thoughts
CVE-2023-23519 shows us that even the safest platforms have vulnerabilities, and sometimes simply _viewing_ a photo is risky if you haven’t patched. Spread the word: keep your gear up to date!
Timeline
Published on: 02/27/2023 20:15:00 UTC
Last modified on: 03/08/2023 15:39:00 UTC