macOS 27: "Enable Keybase in Finder" does nothing — kbfuse 5.0.6 kext refuses to start ("fuse: unsupported kernel version") #29887

Environment

• Keybase 6.6.3-20260603142618+f60f2ff97e
• kbfuse 5.0.6 (/Library/Filesystems/kbfuse.fs)
• macOS 27.3, Apple Silicon (arm64), uname -r = 27.3.0
• Startup security: Reduced Security, 3rd-party kexts enabled; kbfuse is already user-approved and present in the auxiliary kext collection

What happens

Clicking Yes, enable in "Enable Keybase in Finder?" does nothing. /Volumes/Keybase is never mounted. The service log repeats:

KBFS failed to FUSE mount at /Volumes/Keybase (<user>): exit status 2
fuse_status_darwin.go: No kext info available (kext not loaded)

Cause (two layers)

1. No Extensions/27 in the bundle. load_kbfuse looks for Contents/Extensions/<macOS major>/kbfuse.kext. The bundle ships 12 plus symlinks 13, 14, 15, 26 -> 12, so on macOS 27 the loader exits with status 2.

2. The kext itself rejects the kernel. After adding Extensions/27 -> 12 locally:

   $ sudo /Library/Filesystems/kbfuse.fs/Contents/Resources/load_kbfuse
   kext load failed: -603947007
   
   $ sudo kmutil load -b com.github.kbfuse.filesystems.kbfuse
   Kernel request failed: (libkern/kext) kext (kmod) start/stop routine failed (-603946985)
   

   The kext binary contains fuse: unsupported kernel version, and osx/Fuse/build.sh builds it with --kext="12,26.0,25", i.e. Darwin 25 as the highest supported kernel. So the start routine fails on Darwin 27.

Suggested fix

• Rebuild kbfuse with a higher maximum Darwin version in osx/Fuse/build.sh (--kext="12,26.0,25" → a value that covers Darwin 27).
• Add --kext="27->12" and the Contents/Extensions/27 -> 12 symlink, as was done for 13–26.
• Re-sign/notarize the bundle and ship it in the next installer.

A symlink alone is not enough (layer 2), and it breaks the bundle seal (_CodeSignature/CodeResources lists the Extensions/* symlinks), so this needs a rebuild on your side.

Workaround for affected users

KBFS itself works; files are reachable through the Files tab in the app and keybase fs ls|cp|....

Additional numbers

The number 345567