Historically, NULL pointer dereferences have been a significant vulnerability in macOS, allowing attackers to exploit kernel bugs and gain unauthorized access.
A NULL pointer dereference occurs when software attempts to access memory at address 0, which is typically unmapped in modern systems like Apple Silicon.
This results in a memory access fault, causing a Denial of Service (DoS) rather than executing attacker-controlled code.
However, in the past, attackers have exploited these vulnerabilities by mapping controlled memory at address zero, potentially leading to code execution in kernel mode.
Historical Exploitation Techniques
In older macOS versions, particularly on Intel architectures, attackers could exploit NULL pointer dereferences by mapping a fake object at the NULL address in user space.
According to Afine Report, this was possible with 32-bit binaries, where the page-zero reservation could be disabled using specific linker flags.
For example, Piotr Bania from Cisco Talos demonstrated this in 2016 by exploiting an Intel graphics driver bug.
He compiled a 32-bit payload, mapped a page at address zero, and achieved kernel code execution by bypassing SMEP protection.
Another notable example is Luca Todesco’s “tpwn” exploit in 2015, which combined a NULL pointer dereference with an info leak to gain root privileges on OS X Yosemite.
Modern Mitigations
Apple has significantly hardened macOS against such exploits, especially with the transition to Apple Silicon (ARM64 architecture).
Modern macOS versions enforce strict NULL page mapping protections, ensuring that no memory is mapped at address zero in user space.
The kernel also leverages ARMv8 features like Privileged Execute Never (PXN) and Privileged Access Never (PAN), which prevent the kernel from executing user-space code or accessing user memory without explicit overrides.
Additionally, Pointer Authentication Codes (PAC) introduced on ARM64e architectures further 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.
As a result, what was once a potential pathway to kernel exploits is now effectively mitigated, reducing the risk of unauthorized access and code execution.
