CVE-2026-98987: Linux Vulnerability

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.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03, < b9c40553f6ceba50042281eef6f701e5fb719726; >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03, < 87ecd4c6da146363384a603bd9e90c90e7275536; >= 96f5d2e051653f2cfe9137c5d3c7794c358ffb03, < 8714b44adac7b10506e1db3ef1710689751f0f10
Linux	Linux	6.17

References

Timeline

Published: Oct 23, 2026
Last Modified: Oct 23, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-98987?

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.

How severe is CVE-2026-98987?

Severity scoring for CVE-2026-98987 is pending analysis.

How do I fix CVE-2026-98987?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

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