# CVE-2026-98978: namespace: never expire a locked mount


- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** AZL-110807, BELL-CVE-2026-98978, DEBIAN-CVE-2026-98978, GHSA-73pw-3qvg-vxhf, UBUNTU-CVE-2026-98978

## What is CVE-2026-98978?

CVE-2026-98978 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

namespace: never expire a locked mount

Locked mounts are special. They protect the underlying files and
directories from being revealed. do_umount() refuses to unmount locked
mounts but shrink_submounts() doesn't.

A shrinkable mount can become locked once the owner of a user namespace
puts it beneath a locked mount with MOVE_MOUNT_BENEATH. The locked
property now moves to the mount at the bottom making it possible to
unmount the top mount.

So umount() of an unlocked ancestor now expires the bottom mount first
and the covered directory is revealed:

  move_mount(c -> x/hidden, MOVE_MOUNT_BENEATH) = 0
  the cover after the lock moved:  umount2(x/hidden) = 0
  the holder of the lock:          umount2(x/hidden) = EINVAL
  the root of the copy, busy:      umount2(x) = EBUSY
  reads x/hidden/secret: "covered-by-root"

So leave a locked mount alone as it dies together with its parent. A
plain umount() of an unlocked mount with a locked one below it is EBUSY
from now on. It's the same for any other locked child. A lazy umount
still takes the whole tree.

mark_mounts_for_expiry() never sees a locked mount. lock_mnt_tree()
leaves a mount on an expiry list alone and nothing else puts a locked
one on such a list. Add an assert for this.

## Which versions are affected by CVE-2026-98978?


## How do I fix CVE-2026-98978?

Upgrade to a fixed version.

## Is CVE-2026-98978 being exploited?

There is no known exploitation of CVE-2026-98978 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98978 and fix it if it is affected.

What it is: CVE-2026-98978 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98978 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98978/ (Markdown: https://insights.sbomify.com/CVE-2026-98978/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98978
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98978
- OSV: https://osv.dev/vulnerability/CVE-2026-98978

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98978/
Summaries are generated and may contain mistakes; the official description above is the record.