Canonical only released Ubuntu 25.10 Questing Quokka yesterday, but a major issue has already been found (and thankfully fixed); users couldn’t install or update Flatpak applications. According to a bug report on Launchpad, Flatpak installs were failing, displaying a critical error.
The failure was a direct result of changes to the AppArmor security profile for the fusermount3 utility, which is unable to unmount the revokefs-fuse filesystem. The issue was confirmed and affected multiple users.
The root cause of the problem was the fusermount3 utility, which was lacking additional privileges required to function properly in the new confinement setting, specifically failing during the unmounting of the revokefs-fuse filesystem. AppArmor denial logs confirmed that the process was being denied access to files like /run/mount/utab and related files.
To address the bug, AppArmor profile loosening was required. However, this creates some risk. If a user manually modified their profiles, an upgrade might cause conflicts and reject the necessary security fix.
Before the fix was issued, a temporary community-provided workaround was shared, which involved disabling the AppArmor profile for fusermount3 entirely to enable Flatpak usage, however, these shouldn’t be necessary anymore.
Given the wide impacts of the bug, it was marked as Critical importance in the AppArmor package, it has since been updated to Fix Released. To ensure the update reaches users quickly, an SRU (Stable Release Update) was urgently requested for the AppArmor package. The fix involves loosening the AppArmor confinement by adding file access rules, addressing the failure point in Ubuntu 25.10.
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