In the Linux kernel, the following vulnerability has been resolved: namespace: look at the topmost mount for a mount namespace file… (CVE-2026-98987)

The vulnerability in the Linux kernel relates to the attach_recursive_mnt() function, which preallocates a mountpoint for the root of the topmost mount of the source. The issue arises because the loop that walks up the mount chain does not consider the topmost mount itself. If the topmost mount is the only mount namespace file in the chain, the variable 'shorter' remains NULL, causing mnt_change_mountpoint() to attach the existing mount below the root of the mount namespace file (a nsfs dentry). This results in the mount being effectively hidden until its parent is removed, and the copy that replaced it cannot be unmounted synchronously due to having a child mount. The problem manifests in scenarios involving bind mounts and shared/slave mount relationships, leading to unexpected content visibility and EBUSY errors on unmount attempts.

Affected systems may experience mounts becoming inaccessible and inability to synchronously unmount certain mounts, potentially causing resource management issues and operational disruptions related to mount namespace handling. There is no indication of remote code execution or privilege escalation from the provided data.

The vulnerability has been resolved in the Linux kernel. No specific patch links are provided in the input data. Users should apply the official Linux kernel updates that address this issue once available. Patch status is not yet confirmed—check the vendor advisory for current remediation guidance.