CVE-2022-22582 - Symlink Validation Flaw in macOS Allowed Local File Overwrites

Apple scored a solid win for security in spring 2022, but not before a pesky bug – CVE-2022-22582 – put millions of Macs at theoretical risk. Here’s the story behind a subtle but critical validation issue in the way macOS handled symbolic links (symlinks): what went wrong, how it could be exploited by a local user, what Apple did to fix it, and how you can be sure you’re protected.

What was CVE-2022-22582?

CVE-2022-22582 was a local privilege escalation vulnerability in macOS caused by improper validation of symlinks. In simple terms, some processes that wrote files on your Mac didn't check carefully enough where they were really writing. With a crafty symlink placed by a local attacker, it was possible to trick the system into writing data to arbitrary files, which could potentially lead to privilege escalation or system compromise.

Let’s break down the concept

- On Unix-like systems (like macOS), a symlink is a special file that points to another file or folder.
- Some system processes or apps create, read, or write files without always checking if the path is a symlink.
- If an unprivileged local user creates a symlink at a predictable location, and a privileged process writes to that path, the user can make the system write to a target of their choosing.

Example Exploit Scenario

Pretend there’s a system service that regularly writes logs to /tmp/myapp.log. The service runs as root and does something like:

with open("/tmp/myapp.log", "w") as f:
    f.write("Example log data\n")

But what if /tmp/myapp.log isn’t a normal file, but a symlink created by an attacker?

ln -s /etc/passwd /tmp/myapp.log

The next time the service runs, it’ll overwrite /etc/passwd (very bad!), if it didn’t properly check for symlinks.

Proof-of-Concept (PoC) Snippet

Below is a simplified PoC showing how a symlink could be abused before the patch. *Don’t run this on real machines—the consequences are for demonstration only!*

# 1. Create a symlink to a system file (for example, /etc/sudoers)
ln -s /etc/sudoers /tmp/vulnerable.log

# 2. Wait for (or trigger) a process that writes to /tmp/vulnerable.log as root.
# On vulnerable systems, /etc/sudoers gets overwritten!

# 3. After the exploit, you might see that /etc/sudoers is corrupted, which could
# allow privilege escalation or cause denial of service.

In Python (Simulated)

import os

target = '/etc/important_file'
symlink = '/tmp/vuln_symlink'

# Attacker sets up the symlink
os.symlink(target, symlink)

# System process (simulated as running with higher privileges)
with open(symlink, 'w') as f:
    f.write('Oops! System file overwrite\n')

A local attacker could overwrite system configuration files.

- Exploitation could result in escalation of privileges, denial of service, or persistent system compromise.

What Did Apple Do?

Apple’s fix: They improved the logic so the system now properly checks whether a target is a symlink before opening it, ensuring privileged processes can’t be tricked.

macOS Monterey 12.3

> Reference:
> Apple Security Updates - CVE-2022-22582
> NVD Description

Mitigation & How To Stay Safe

- Update your Mac. If you’re running any version before the patched releases above, go to the Apple Menu → System Preferences → Software Update and get the latest.
- Don’t ignore security patches. These types of local bugs are often paired with other exploits in real malware attacks.

Conclusion

CVE-2022-22582 is a classic example of how something as seemingly minor as symlink handling can open the door to serious compromise. Thanks to Apple’s patching and the watchful eyes of security researchers, most Mac users are now protected. But it’s a reminder: symlink attacks are easy to miss and can be seriously dangerous. Always keep your systems updated!

Timeline

Published on: 02/27/2023 20:15:00 UTC
Last modified on: 03/07/2023 20:21:00 UTC