CVE-2023-32434 - The Apple Kernel Integer Overflow Vulnerability Exploited in the Wild

Security vulnerabilities continue to pose significant threats to users across platforms, and Apple devices are no exception. One of the significant vulnerabilities disclosed in 2023 was CVE-2023-32434, an integer overflow bug affecting the kernel component of multiple Apple operating systems. This issue was so severe that it allowed applications to execute arbitrary code with kernel privileges—a worst-case scenario for security. Even more concerning, Apple admitted the flaw may have been actively exploited "in the wild" before it was patched, particularly targeting older iOS versions.

In this post, we break down what CVE-2023-32434 is, how it could be exploited, and how Apple fixed it. We’ll also offer code snippets showing how these bugs can arise, and provide links to original resources for deeper review. The language used here avoids jargon as much as possible, so anyone interested in security can understand how this kind of bug works.

What Is CVE-2023-32434?

CVE-2023-32434 is an integer overflow vulnerability in the Apple kernel. This means that certain arithmetic operations in code could produce results larger than expected, "wrapping around" and resulting in inadequate memory allocations or buffer overflows.

This vulnerability was especially impactful because an application could use this weakness to run its own code with kernel privileges. The kernel is the core part of any operating system, and code running at this level can do almost anything: read all user data, bypass security controls, and brick or permanently infect a device.

Apple’s Security Advisory:  
https://support.apple.com/en-us/HT213751

iOS & iPadOS: 15.7.7, 16.5.1

If you are running an earlier version, upgrade immediately! For reference:  
https://support.apple.com/en-us/HT201222

How Does Integer Overflow Work?

Imagine asking for a bowl that can hold 10 apples, but you try to put in 300 apples. If the bowl-readers use only one decimal digit to count and don’t check properly, their count “wraps around” after 9—so “300 apples” ends up looking like “ apples” to them, and they only give you a tiny bowl. You can then overflow apples onto the table.

In computer terms, if a function multiplies two integers (say, requested element size by element count) and the result is larger than the type can hold, it “wraps around” to zero or a small value.

Example (Pseudocode)

// Vulnerable allocation
size_t count = user_input_count;
size_t size = sizeof(struct foo);

size_t total = count * size;
void* buffer = malloc(total);
// If count is very large, total can overflow to a small value!

If count is large enough, total becomes much smaller than intended. This causes the program to allocate a small buffer, but later fills it as if it was big, writing out-of-bounds and corrupting memory.

According to Apple (source)

> Impact: An app may be able to execute arbitrary code with kernel privileges.  
> Description: An integer overflow was addressed with improved input validation.  
> Apple is aware of a report that this issue may have been actively exploited against versions of iOS released before iOS 15.7.

Exploit Details Overview

While Apple and independent researchers have not published full proof-of-concept code (for safety reasons), the general exploitation path is understood.

Exploitation Steps

1. Malicious App (or code running in an app) sends data to a vulnerable kernel API, supplying large values for counts or sizes.
2. The kernel code multiplies these values, expecting to allocate enough memory, but the multiplication overflows and allocates too little memory.
3. The kernel then copies user-supplied data into the buffer, overflowing into adjacent kernel memory ("buffer overflow").

Cleverly crafted data can overwrite function pointers or control data used by the kernel.

5. When the kernel later uses the overwritten data, the attacker’s payload is executed with kernel privileges.

Proof-of-Concept Snippet

For security reasons, we won't supply a working exploit, but here's how such a bug could look in a simplified C kernel module.

void process_request(user_req *req) {
    // Example vulnerable calculation
    size_t alloc_size = req->count * sizeof(struct thing);
    struct thing *buf = (struct thing *)malloc(alloc_size);
    if (!buf) return;

    // Kernel copies 'count' items from user data
    memcpy(buf, req->user_data, req->count * sizeof(struct thing));
    // If alloc_size overflowed, memcpy overflows buf!
}

An attacker would submit a count high enough that alloc_size wraps around and becomes a small value, causing a buffer overflow in the kernel.

Real-World Impacts

Any app could use this flaw to escape sandboxing and gain full device control.

The seriousness is underscored by Apple's acknowledgment of active exploitation before the public patch. Attackers may have targeted spy victims, high-value individuals, or general users with malware-laced apps or other remote vectors.

Ensuring that allocations use safe APIs which check for overflows.

- Testing whether calculated sizes are actually valid before using them in memory allocations or copy operations.

Fixed Pseudocode

// Fixed: Check for overflow before allocation
size_t count = req->count;
if (count > SIZE_MAX / sizeof(struct thing)) {
    // Invalid input, handle error
    return;
}
size_t alloc_size = count * sizeof(struct thing);
struct thing* buf = malloc(alloc_size);

References

- Apple Security Advisory – HT213751 (CVE-2023-32434)
- Apple Security Updates – Comprehensive List
- CVE Record for CVE-2023-32434 on MITRE

Conclusion

CVE-2023-32434 shows how a simple arithmetic bug in deep, trusted code can have massive consequences—potentially giving attackers full control of millions of devices. Apple’s quick patching (across multiple OS versions) reflects the gravity of the flaw, especially given signs of real-world exploitation. Always keep your devices updated, and be wary of installing apps from untrusted sources.

Stay safe, and keep your Apple devices patched!

*This article is exclusive original writing for your request, summarizing public data in a simple, clear way for everyone.*

Timeline

Published on: 06/23/2023 18:15:13 UTC
Last modified on: 10/25/2023 23:15:16 UTC