Live › vulnerability › CVE-2026-98979
Go to dashboardA flaw in the Linux kernel's mount handling lets an automount be attached below a mount that is in no namespace, which dereferences an error pointer and crashes the kernel. The reported trigger is opening a path reported by fanotify on an overlay's lower filesystem, after which all mount operations on the system block.
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 fanotify filesystem marks on a lower filesystem beneath an overlay mount, or that otherwise allow unprivileged users to trigger automounts. Hosts without overlay layers or fanotify watchers on such filesystems are less likely to be exposed, but the sources do not say which configurations are required.
No product ranges from the sources yet.
uname -r and compare against the fixed kernel versions listed in the NVD entry (unknown in the sources).attach_recursive_mnt / is_mounted() in fs/namespace.c (unknown in the sources).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: refuse an automount below a mount that is in no namespace
It's possible to add autmounts even when the parent mount isn't in the mount namespace of the caller. The only requirement we have is that the parent mount namespace must not be NULL, i.e., unmounted.
Problem is that clone_private_mount() has MNT_NS_INTERNAL which makes that trivially true. So that passes the test and attach_recursive_mnt() accepts that as a mount point and funny enough, count_mounts() dereferences MNT_NS_INTERNAL. The problem is it is an error pointer...
So we can reach this in userspace via fanotify. A filesystem mark on the lower filesystem of an overlay reports paths on the layer clone and reading the event hands out a descriptor on it. For example with debugfs as the lower layer it goes kaboom:
openat(evfd, "tracing", O_DIRECTORY)
Oops: general protection fault KASAN: null-ptr-deref in range [0x1d0-0x1d7] RIP: 0010:count_mounts+0x35/0x200 attach_recursive_mnt finish_automount
And since that sleeping beauty happens under namespace_sem held for writing every mount operation on the system blocks from then on. Congrats.
Use is_mounted() instead which rejects unmounted and internal mounts alike. The open fails with EINVAL just as it did before clone_private_mount() used MNT_NS_INTERNAL.
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