# CVE-2026-98979: namespace: refuse an automount below a mount that is in no namespace


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110810, BELL-CVE-2026-98979, DEBIAN-CVE-2026-98979, GHSA-xhgj-mp6g-fw2x, UBUNTU-CVE-2026-98979

## What is CVE-2026-98979?

CVE-2026-98979 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

namespace: refuse an automount below a mount that is in no namespace

It's possible to add autmounts even when the parent mount isn't in the
mount namespace of the caller. The only requirement we have is that the
parent mount namespace must not be NULL, i.e., unmounted.

Problem is that clone_private_mount() has MNT_NS_INTERNAL which makes
that trivially true. So that passes the test and attach_recursive_mnt()
accepts that as a mount point and funny enough, count_mounts()
dereferences MNT_NS_INTERNAL. The problem is it is an error pointer...

So we can reach this in userspace via fanotify. A filesystem mark on the
lower filesystem of an overlay reports paths on the layer clone and
reading the event hands out a descriptor on it. For example with debugfs
as the lower layer it goes kaboom:

  openat(evfd, "tracing", O_DIRECTORY)

  Oops: general protection fault
  KASAN: null-ptr-deref in range [0x1d0-0x1d7]
  RIP: 0010:count_mounts+0x35/0x200
   attach_recursive_mnt
   finish_automount

And since that sleeping beauty happens under namespace_sem held for
writing every mount operation on the system blocks from then on.
Congrats.

Use is_mounted() instead which rejects unmounted and internal mounts
alike. The open fails with EINVAL just as it did before
clone_private_mount() used MNT_NS_INTERNAL.

## Which versions are affected by CVE-2026-98979?


## How do I fix CVE-2026-98979?

Upgrade to a fixed version.

## Is CVE-2026-98979 being exploited?

There is no known exploitation of CVE-2026-98979 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98979 and fix it if it is affected.

What it is: CVE-2026-98979 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98979 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-2026-98979/ (Markdown: https://insights.sbomify.com/CVE-2026-98979/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98979
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98979
- OSV: https://osv.dev/vulnerability/CVE-2026-98979

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98979/
Summaries are generated and may contain mistakes; the official description above is the record.