macOS 26.4 Beta: Problems Mounting HFS+ Volumes

I normally don’t write about beta bugs, but I’ve seen lots of people discussing this one and also received customer questions about it. I can reproduce it on my Mac, though not for every HFS+ volume.

Apple:

HFS external media might fail to mount automatically. (168672160)

Workaround: For macOS only, use CLI tool diskutil mount to attach the relevant disk device.

This also affects disk images, both creating them and mounting them on macOS 26.4 (even if they were created using another version). I discuss some workarounds for DropDMG here.

Thomas Rohde (Reddit, MacRumors, 2):

Apparently fsck_hfs is broken

Mr. Macintosh:

I tried to warn as many people as possible about HFS issues but I did not at the time know it was fsck.

Thomas Rohde:

I have 7 (seven!) external drives that I currently can’t use 🙄

Corentin Cras-Méneur:

Finally figured out how to properly mount my external HFS drives under macOS 26.4b1! diskutil mount—suggested as a workaround in the release notes—was SURE not cutting it. I had to use sudo mount -t hfs instead (specifying the filesystem format and mount path manually). What a pain it was!

[…]

They are all standard hard drives and I never migrated them to APFS because I didn’t want the loss of performance (plus, I’ve seen some pretty nasty corruptions on APFS that were really REALLY hard to recover from while I have my faithful DiskWarrior for HFS+).

Previously:

• APFS Enumeration Performance on Rotational Hard Drives

Bug Disk Image DropDMG HFS+ Mac macOS Tahoe 26 Storage

Outlook Copilot Bug Exposes Confidential E-mails

Sergiu Gatlan (Hacker News):

Microsoft says a Microsoft 365 Copilot bug has been causing the AI assistant to summarize confidential emails since late January, bypassing data loss prevention (DLP) policies that organizations rely on to protect sensitive information.

[…]

“A code issue is allowing items in the sent items and draft folders to be picked up by Copilot even though confidential labels are set in place,” Microsoft added.

Thomas Claburn:

It’s just this sort of scenario that has led 72 percent of S&P 500 companies to cite AI as a material risk in regulatory filings.

[…]

“Although content with the configured sensitivity label will be excluded from Microsoft 365 Copilot in the named Office apps, the content remains available to Microsoft 365 Copilot for other scenarios,” the documentation explains. “For example, in Teams, and in Microsoft 365 Copilot Chat.”

[…]

In theory, DLP policies should be able to affect Microsoft 365 Copilot and Copilot Chat. But that hasn’t been happening in this instance.

Previously:

• Microsoft Rust and Copilot
• Microsoft Australia Refunds for Office/Copilot Dark Pattern
• Forcing Copilot AI
• Opting Out of Microsoft 365’s Copilot AI
• Privacy of Windows Copilot+ Recall
• Microsoft 365 Copilot

Artificial Intelligence Bug Copilot AI E-mail Mac Mac App macOS Tahoe 26 Microsoft Office Microsoft Outlook Privacy Windows Windows 11