# CVE-2026-98987: namespace: look at the topmost mount for a mount namespace file


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** BELL-CVE-2026-98987, DEBIAN-CVE-2026-98987, GHSA-8fp8-xwh3-vf8f, UBUNTU-CVE-2026-98987

## What is CVE-2026-98987?

CVE-2026-98987 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official 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.

## Which versions are affected by CVE-2026-98987?


## How do I fix CVE-2026-98987?

Upgrade to a fixed version.

## Is CVE-2026-98987 being exploited?

There is no known exploitation of CVE-2026-98987 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98987 and fix it if it is affected.

What it is: CVE-2026-98987 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98987 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-2026-98987/ (Markdown: https://insights.sbomify.com/CVE-2026-98987/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98987
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98987
- OSV: https://osv.dev/vulnerability/CVE-2026-98987

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98987/
Summaries are generated and may contain mistakes; the official description above is the record.