CVE-2026-98987 namespace: look at the topmost mount for a mount namespace file
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-98987?
CVE-2026-98987 is a vulnerability in Linux, published on 23 Oct 2026.
Official description
In the Linux kernel, the following vulnerability has been resolved:
namespace: look at the topmost mount for a mount namespace file
attach_recursive_mnt() preallocates a mountpoint for the root of the topmost mount of the source so that a mount that already sits at the destination can be put on top of the source or on top of one of its propagated copies.
The copies are made without CL_COPY_MNT_NS_FILE so their chain of overmounts is shorter than the source's. It ends below the first bind mount of a mount namespace file. So while the loop walks up the chain of the source it remembers the mountpoint of that mount in "shorter" and the existing mount is put there for the copies.
But the loop ends at the topmost mount without ever looking at it. If the topmost mount is the only mount namespace file in the chain "shorter" stays NULL and mnt_change_mountpoint() attaches the existing mount of the copy below the root of the mount namespace file. That's a dentry of nsfs. No path walk in the copy's mount namespace ever gets there. The mount is gone until its parent goes and the copy that took its place can't be unmounted synchronously because it has a child:
S bind mount of a file N bind mount of a mount namespace file on top of S A shared mount, B a slave of A, Q mounted on B/file
move_mount(S, A/file) cat B/file -> the content of S instead of Q umount B/file -> EBUSY
Look at every mount of the chain including the topmost one.
Which versions are affected by CVE-2026-98987?
How do I fix CVE-2026-98987?
Upgrade to a fixed version.
Is CVE-2026-98987 being exploited?
There is no known exploitation of CVE-2026-98987 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98987, DEBIAN-CVE-2026-98987, GHSA-8fp8-xwh3-vf8f, UBUNTU-CVE-2026-98987.