# CVE-2026-98976: namespace: keep the lock on a mount that a propagated copy is moved beneath


- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98976, GHSA-38fm-jc3c-v2pm, UBUNTU-CVE-2026-98976

## What is CVE-2026-98976?

CVE-2026-98976 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: keep the lock on a mount that a propagated copy is moved beneath

attach_recursive_mnt() transfers MNT_LOCKED from the top mount to the
mount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the
owner of a user namespace to replace its locked /proc or its root. The
mount beneath takes on the job of covering the underlying mountpoint
allowing the top mount to be unmounted.

Consider two mount namespaces:

(H) The host H has a shared mount P with a secret in P/d
(Z) Z is a user namespace made from M. Its copy of P receives
    propagation from the host's P and its copy of M's cover on P/d is
    locked Z's owner must not get to see P/d.

Now (H) mounts X on P/d. This propagates into (Z). The copy of X lands
beneath (Z)'s locked cover. The locked property is transfered from (Z)'s
cover to the copy of X propagated beneath it. The cover is now unlocked.

Now (H) unmounts X again. The copy of X in (Z) gets unmounted and the
covering mount is left unlocked on top of P/d. (Z) can now unmount it:

    Z: umount2(P/d)             = EINVAL            /* the cover is locked */
    H: mount X on P/d, umount X                     /* both propagate into Z /*
    Z: umount2(P/d)             = 0                 /* the cover is now unlocked */
    Z: read P/d/secret          = "covered-by-root" /* secret revealed */

So only transfer the locked property to the mount beneath for mounts the
caller has placed. A propagated copy that lands beneath a locked mount
is locked as well so that the mount at the bottom of the stack carries a
lock the way every check expects. The mount on top of it remains locked
to ensure that it keeps covering even if the propagated mount is
unmounted again.

## Which versions are affected by CVE-2026-98976?


## How do I fix CVE-2026-98976?

Upgrade to a fixed version.

## Is CVE-2026-98976 being exploited?

There is no known exploitation of CVE-2026-98976 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98976 and fix it if it is affected.

What it is: CVE-2026-98976 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98976 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-2026-98976/ (Markdown: https://insights.sbomify.com/CVE-2026-98976/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98976
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98976
- OSV: https://osv.dev/vulnerability/CVE-2026-98976

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98976/
Summaries are generated and may contain mistakes; the official description above is the record.