Security Experts:

Patch for macOS Root Access Flaw Breaks File Sharing

The patch released by Apple on Wednesday for a critical root access vulnerability affecting macOS High Sierra appears to break the operating system’s file sharing functionality in some cases. The company has provided an easy fix for affected users.

The flaw, tracked as CVE-2017-13872, allows an attacker to gain privileged access to a device running macOS High Sierra by logging in to the root account via the graphical user interface with the username “root” and any password. Apple has disabled the root account by default and when users attempt to log in to this account, the password they enter is set as its password. If the password field is left blank, there will be no password on the root account.

The vulnerability can be exploited locally, but remote attacks are also possible if sharing services are enabled on the targeted machine.

While the issue was mentioned on Apple developer forums on November 13, the tech giant only learned about it on November 28, when a Turkish developer posted a message on Twitter. A patch was released within 24 hours, but since Apple did not have enough time to test the fix, it appears to introduce other problems.

Some users may find that the file sharing functionality no longer works after they have installed the security update for High Sierra 10.13.1.

An advisory published by Apple shortly after the release of the update provides recommendations on how to repair file sharing. Users simply need to open the Terminal, type the command sudo /usr/libexec/configureLocalKDC, and enter their administrator password when prompted. This should address the issue until Apple releases another update.

Attacks exploiting CVE-2017-13872 can also be prevented by manually setting a password for the root user account or disabling sharing services if not needed. Apple said the security hole does not affect macOS Sierra 10.12.6 and earlier.

This is not the only authentication bug found in macOS High Sierra recently. Last month, a developer noticed that the operating system had leaked the passwords for encrypted Apple File System (APFS) volumes via the password hint.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.