CVE-2026-98992 namespace: don't copy an unmounted mount tree

Q: Is CVE-2026-98992 being exploited?

There is no known exploitation of CVE-2026-98992 in the wild and no public exploit code.

Not scored Published 23 Oct 2026 Updated 23 Oct 2026

Exploited in the wild: Not known
Fix: Available

What is CVE-2026-98992?

CVE-2026-98992 is a vulnerability in Linux, published on 23 Oct 2026.

Official description

In the Linux kernel, the following vulnerability has been resolved:

namespace: don't copy an unmounted mount tree

may_copy_tree() accepts a mount whose root is an nsfs or pidfs file before it checks whether that mount is mounted. This exception exists for nsfs and pidfs mounts. They are part of no mount namespace so neither check_mnt() nor is_mounted() would let them through and bind-mounting a nsfsfd or a pidfd wouldn't work.

Problem is that exception also admits a bind mount of such a file when it was lazily unmounted and is only kept alive by a file descriptor:

mount --bind /proc/self/ns/net /tmp/x exec 3< /tmp/x umount -l /tmp/x mount --rbind /proc/self/fd/3 /tmp/y

With MS_REC or AT_RECURSIVE copy_tree() doesn't stop at the unmounted mount. It copies every mount that stayed attached to it as well. So if you have a bunch of overmounts over the nsfsfd or the pidfd the whole unmounted stack is copied. That's a bug.

So refuse to walk an unmounted tree. Copying its root alone stays possible. So a bind mount of a namespace that is gone can still be recreated from a file descriptor on the old one. The file descriptor pins that mount and its root and __has_locked_children() only reads the direct children which don't leave the parent's list without namespace_sem. The internal mounts carry MNT_NS_INTERNAL instead of NULL and are still walked. Copying an unmounted tree recursively fails with EINVAL.

Which versions are affected by CVE-2026-98992?

How do I fix CVE-2026-98992?

Upgrade to a fixed version.

Is CVE-2026-98992 being exploited?