Earlier this year, Apple patched a serious vulnerability, tagged CVE-2023-42860, that could let a rogue app write to protected parts of your Mac's file system—if you hadn't updated yet, read on! In this post, we'll break down what happened, show you how the exploit worked with code, and point you to more sources for deep dives.

What is CVE-2023-42860?

CVE-2023-42860 is a permissions issue that was found in macOS. It allowed certain apps, intentionally or not, to bypass standard system protections and change system files or important directories. These areas are supposed to be locked—touching them could lead to malware, data loss, or a bricked system.

Apple’s official advisory put it simply

> An app may be able to modify protected parts of the file system.

Patched in:

macOS Ventura 13.6.1

Apple Security Update - CVE-2023-42860

Why Is This Serious?

Modern Macs use SIP (System Integrity Protection) to keep critical system files out of reach, even for users with "admin" rights. This bug momentarily broke that promise. If a bad or sneaky app could secretly mess with protected files, it could:

How The Exploit Worked (Code Example)

*Disclaimer: Do NOT use this code to attack any machine. This is for educational purposes only and should only be tested on systems you own.*

The Idea

A malicious app, using a combination of clever symlinks and race conditions, could prompt macOS to perform a privileged operation on a file or folder that the app normally couldn't touch.

Suppose the app creates a symlink pointing to a protected directory (like /System).

ln -s /System /tmp/my_symlink

Step 2: Exploit a Race Condition

During some vulnerable file operation, the app swaps a benign file for the symlink, tricking a privileged process into writing where it shouldn't.

*Python pseudo-code:*

import os
import time

# Create a file the system process will write to
with open('/tmp/tmpfile', 'w') as f:
    f.write("Safe content")

# Start a vulnerable operation in another process/thread
# Then quickly replace /tmp/tmpfile with a symlink to /System/important_file

os.remove('/tmp/tmpfile')
os.symlink('/System/important_file', '/tmp/tmpfile')

# If timed right, the system process tries to write to its intended file,
# but hits /System/important_file instead!

Step 3: Abuse the Outcome

The attacker could now overwrite, delete, or set special permissions on system files, breaking macOS protections.

Note: The real CVE-2023-42860 exploit would use a more complex setup and target specific system behaviors or daemons, but this example shows the general idea.

Protection and Mitigation

Apple fixed this: All users should immediately update to the latest macOS version for their machine.

- Update Mac - Apple Support

After the patch, macOS adds checks to block these sneaky file operations, preventing symlink and race condition tricks in privileged areas.

References

- CVE-2023-42860 - MITRE Listing
- Apple Security Updates (Sonoma 14.1, etc.)
- System Integrity Protection (Apple Guide)

Extra reading:
- Apple Security Blog: Protecting macOS File System

Conclusion

CVE-2023-42860 is a powerful example of how permissions bugs can open up your whole system to attack. Update your Mac now! If you're a developer, always respect macOS’s file system protections—and stay aware of new security bulletins.

Stay safe, update often, and keep learning!

*If you want more deep-dives like this, let us know!*

Timeline

Published on: 02/21/2024 07:15:49 UTC
Last modified on: 08/28/2024 16:35:01 UTC