Microsoft gives Apple a migraine

On May 18, 2023, Apple published security content for macOS Ventura 13.4, macOS Monterey 12.6.6, and macOS Big Sur 11.7.7 that addressed a logic issue in libxpc.

The Common Vulnerabilities and Exposures (CVE) database lists publicly disclosed computer security flaws. The CVE we are going to discuss is listed as CVE-2023-32369, which allows an app to modify protected parts of the macOS file system.

At the time there were no other details provided. This is usual and done to give users ample time to implement the necessary patches. But now Microsoft has published a blogpost that provides details about the vulnerability and how it was discovered during a routine malware hunt.

The updates may already have reached you in your regular update routines, but it doesn’t hurt to check if your device is at the latest update level. If not, you can follow the instructions on how to update macOS on Mac.

libxpc is a closed source project that is part of XPC, which is the enhanced inter-process communication (IPC) framework used in macOS/iOS. In computer science, IPC refers specifically to the mechanisms an operating system provides to allow processes to manage shared data.

One of the security related functions of libxpc is System Integrity Protection (SIP). SIP is a security technology designed to help prevent potentially malicious software from modifying protected files and folders on your Mac. System Integrity Protection restricts the root user account and limits the actions that the root user can perform on protected parts of the Mac operating system. SIP is enabled by default on all modern macOS software releases.

This means that only certain processes—signed by Apple—have special entitlements to write to protected parts of macOS. This includes things like Apple software updates and Apple installers.

The Microsoft security engineers that are credited in the Apple security content however, found a flaw that allowed attackers with root permissions to add a malicious payload to SIP’s exclusions list and launch it. Because they managed to pull this off by abusing the macOS Migration Assistant utility, they named the vulnerability Migraine.

Successfully exploiting this vulnerability would allow an attacker that had somehow managed to obtain root privileges to install a rootkit which would be protected by SIP. SIP can only be disabled by following this procedure:

1. Restart your system in Recovery mode.
2. Launch Terminal from the Utilities menu.
3. Run the command csrutil disable.
4. Restart your system.

Because SIP is controlled through the Mac’s NVRAM, enabling or disabling SIP affects all versions of the Mac operating system that are installed on the system. NVRAM (nonvolatile random-access memory) is a small amount of memory that your Mac uses to store certain settings and access them quickly.

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