Live › vulnerability › CVE-2026-98992
Go to dashboardThe Linux kernel let a recursive bind mount copy a lazily unmounted mount tree rooted at an nsfs or pidfd file, which it should not walk. The fix refuses recursive copies of unmounted trees, so the kernel no longer duplicates mounts that stayed attached to the unmounted one.
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 the upstream fix that handle nsfs or pidfd bind mounts, typically hosts where unprivileged or container workloads can create mounts from file descriptors. The sources do not say which kernel versions are affected or which configurations are exposed, so teams should check their distribution's advisory.
No product ranges from the sources yet.
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: 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.
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