macOS NULL Pointer Dereference Vulnerability Allow Attackers Exploits Kernel

Historically, NULL pointer dereferences have been a significant vulnerability in operating systems, including macOS.

These occur when software attempts to access memory at address 0 via a NULL pointer, leading to potential crashes or, under certain conditions, exploitation by attackers.

In the past, attackers could exploit such vulnerabilities by mapping controlled memory at address 0, allowing them to execute arbitrary code in kernel mode.

Historical Exploitation Techniques

In older macOS versions, particularly on Intel architectures, attackers exploited NULL pointer dereferences by mapping fake objects at the NULL address in user space.

This was possible with 32-bit binaries, where the page-zero reservation could be disabled, allowing memory allocation at address 0.

Notable examples include Piotr Bania’s exploit of an Intel graphics driver bug in 2016 and Luca Todesco’s “tpwn” exploit in 2015, which targeted OS X Yosemite.

According to Afine Report, these exploits often required bypassing protections like SMEP (Supervisor Mode Execution Prevention), which prevents the kernel from executing user-space memory.

However, Apple has significantly hardened macOS against such exploits.

Starting with OS X 10.11 (El Capitan), Apple introduced SMEP and other hardening measures, including System Integrity Protection (SIP).

By late 2016, Apple had effectively closed avenues for exploiting NULL pointer dereferences by adding NULL checks and improving state handling.

The removal of 32-bit process support in macOS 10.15 further eliminated the primary method for mapping the NULL page on Intel-based machines.

Modern Mitigations on Apple Silicon

The transition to Apple Silicon (ARM64 architecture) has introduced robust mitigations that render NULL pointer dereferences unexploitable.

On Apple Silicon, all user processes are 64-bit, and the kernel enforces strict NULL page mapping protections, ensuring that no memory is mapped at address 0 in user space.

The ARM64 architecture leverages features like Privileged Execute Never (PXN) and Privileged Access Never (PAN), which prevent the kernel from executing code from user-space pages and accessing user memory without explicit overrides.

Additionally, Pointer Authentication Codes (PAC) on ARM64e architecture protect against pointer corruption by verifying cryptographic signatures on pointer values.

These enhancements make it extremely difficult for attackers to exploit NULL pointer dereferences on modern macOS systems.

Any attempt to do so would result in a fault rather than code execution, effectively halting potential exploits.

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