Cloudanix VulnDB

CVE-2026-98987

None

CVSS

—

EPSS

0.2%

Published

Oct 23, 2026

CISA due date

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Cloudanix analysis

Next patch cycle SSVC: Track

A Linux kernel bug in handling certain mount operations could let one process see files belonging to another isolated environment.

Exploitation
Local Privilege
Attacker needs
Local User
Complexity
Moderate
Impact
Data Exposure
Component
OS kernel
Class
Information Disclosure
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Incorrect mountpoint selection in attach_recursive_mnt() when the topmost mount is a mount namespace file causes mnt_change_mountpoint() to attach an existing mount below the root of an nsfs dentry instead of the intended location, resulting in wrong file content exposure across bind mounts and mount namespaces.

Why it matters to the business

Attackers may read file contents belonging to other mount namespaces or shared mounts, undermining isolation guarantees and potentially leaking sensitive data; unmount operations can fail with EBUSY, disrupting container or namespace-based workloads.

How an attack unfolds

An attacker creates a chain of bind mounts including a mount namespace file, sets up shared and slave mounts, performs a move_mount operation, then reads or unmounts the target to observe content from an unintended source mount due to the missing topmost-mount check.

How to fix it

Apply the upstream kernel patch that extends the loop in attach_recursive_mnt() to examine the topmost mount; rebuild and deploy updated kernel packages; reboot affected systems.

How to confirm the fix worked

Confirm kernel source contains the updated attach_recursive_mnt() logic that inspects every mount including the topmost one; test the provided reproducer sequence to verify correct file content and successful unmount.

Typical attack path

  1. Create source bind mount S of a file
  2. Create mount namespace file bind mount N on top of S
  3. Establish shared mount A with slave B and mount Q on B/file
  4. Issue move_mount(S, A/file)
  5. Read B/file to obtain content of S instead of Q
  6. Attempt umount on B/file to observe EBUSY

How to detect it

Search kernel logs and audit trails for unexpected mount namespace file references, failed umount calls returning EBUSY on nsfs paths, or processes reading from bind-mounted namespace files after move_mount operations.

What your security team should do

  • Prioritize kernel updates on systems using containers or mount namespaces
  • Monitor upstream stable branches for the released fix
  • Review workloads that rely on bind mounts of /proc/*/ns/* files for isolation

The record

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 packages

Ecosystem Package Introduced Fixed