Apple macOS issues reveal passwords for APFS encrypted volumes in plaintext

Pierluigi Paganini April 01, 2018

A security expert discovered severe security issues in APFS file system for macOS High Sierra that expose passwords of encrypted external drives in plain text.

A vulnerability in APFS file system for macOS High Sierra operating system has been discovered by forensic analyst Sarah Edwards.

According to Edwards, the flaw exposes passwords of encrypted external drives in plain text.

Apple File System (APFS) is a proprietary file system for macOS High Sierra and later, iOS 10.3 and later, tvOS 10.2 and later, and watchOS 3.2 and later, developed and deployed by Apple Inc. APFS is optimized for flash solid-state drive storage, it aims to improve encryption and performance.

The flaw leaves encryption password for a newly created APFS volume in the unified logs in plaintext, it also allows encrypting previously created but unencrypted volumes.

“I’ve been updating my course (Mac and iOS Forensics and Incident Response) to use new APFS disk images (APFS FTW!) and came across something that both incredibly useful from a forensics perspective but utterly horrifying from a security standpoint. Screenshot below of my course disk image.” states the blog post published by Edwards.

APFS flaw

“It may not be noticeable at first (apart from the highlighting I’ve added of course), but the text “frogger13” is the password I used on a newly created APFS formatted FileVault Encrypted USB drive with the volume name “SEKRET”. (The new class images have a WarGames theme, hence the shout-outs to classic video games!)”

This means that anyone with access to the machine can see passwords stored in plaintext, the experts also warned that a malware could be used to collect log files to gather passphrase.

The password for an encrypted APFS volume can be retrieved by running e executing the following ‘newfs_apfs’ command in the terminal:

log stream --info --predicate 'eventMessage contains "newfs_"'

Edwards updated her post to highlight that she has discovered similar log entries in another system log that is more persistent.

“In and update to my previously updated blog article, I have found another instance where the plaintext password was written to system logs. This time I found it in more persistent log. This is actually a worse problem than the one I previously reported on.” he wrote in a new blog post.
“The previous examples were found in the unified logs which can hang around for a few weeks, this new example stores the exact same information in the system’s /var/log/install.log. I have found that the install.log will only get wiped out upon major re-installation (ie: 10.11 -> 10.12 -> 10.13), “

APFS flaw 2

Edwards pointed out that after the Twitter user @sirkkalap announced he was unable to re-create the issue she had previously reported, she was also unable to reproduce it.

“I assumed that at some point in the past few days a silent security update was pushed out. I went to my install.log file to investigate further. As far as updates go – the only thing that has potential to be the cause of the fix is a GateKeeper ConfigData update v138 (” said Edwards.

The expert highlighted that you would not find the password in the plaintext when converting a non-APFS drive to APFS and then encrypt the drive.

The flaw affects only macOS 10.13 and 10.13.1, while later versions of macOS High Sierra have somehow reportedly addressed the issue.

In the past months, other two issues were discovered in the APFS, in February the Apple expert Mike Bombich discovered an APFS Filesystem vulnerability that could lead macOS losing data under certain conditions. In October 2017, Apple released a patch for macOS High Sierra 10.13 that addressed also a flaw in Apple file system that exposes encrypted drive’s password in the hint box.

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Pierluigi Paganini

(Security Affairs – APFS Filesystem, hacking)

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