Live › vulnerability › CVE-2026-98990
Go to dashboardA race in the Linux kernel's mount handling lets a synchronous umount remove a mount that is still in use elsewhere, because the busy check runs before an earlier unmount changes the mount tree. The sources do not say what an attacker gains beyond disrupting mounts such as NFS, AFS, CIFS or tracefs automounts.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Systems running a Linux kernel without this fix that use automounted submounts (NFS, AFS, CIFS) or the tracefs mount beneath debugfs, since bind mounts inherit the flag. The sources do not say who can trigger the umount, so the exposure of multi-user hosts is unknown.
No product ranges from the sources yet.
uname -r and compare against the fixed kernel version in the vendor advisory (unknown from these sources).findmnt -o TARGET,FSTYPE,PROPAGATION.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
In the Linux kernel, the following vulnerability has been resolved:
namespace: check a submount for references right before unmounting it
shrink_submounts() and mark_mounts_for_expiry() first collect all the mounts they are allowed to unmount and then unmount them.
Whether a mount is busy is decided by propagate_mount_busy() on the tree. But unmounting the first mount changes the tree that the second one propagates into. propagate_umount() moves a surviving overmount off a copy it unmounts and mounts it where the copy was mounted. If that's where the propagated copy of the second victim is looked up the overmount becomes a candidate of the second umount_tree(). It's childless and so trim_one() commits it without looking at its reference count.
So a synchronous umount pulls out a busy mount that is in use somewhere else and marks it MNT_SYNC_UMOUNT while it has users:
umount2(/tmp/plshrink/p1, 0) = 0 errno 0 cwd is (unreachable)
The same two umounts requested one after the other fail with EBUSY. This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts inherit the flag.
Check each mount right before it is unmounted under the same hold of namespace_sem and mount_lock as the umount itself. Make sure that the algorithm stays linear.
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