# CVE-2026-98983: unshare: don't drop active namespace references that were never taken


- **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-2026-98983, DEBIAN-CVE-2026-98983, GHSA-vc4v-q632-x9g5, UBUNTU-CVE-2026-98983

## What is CVE-2026-98983?

CVE-2026-98983 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

unshare: don't drop active namespace references that were never taken

Active references on the namespaces of an nsproxy are taken when the
nsproxy is installed into a task in switch_task_namespaces() and
copy_namespaces() and dropped again by put_nsproxy() through
deactivate_nsproxy().

But ksys_unshare() calls put_nsproxy() on an nsproxy that was never
installed when set_cred_ucounts() fails. The new namespaces of that
nsproxy go from zero to minus one and the namespaces shared with the
caller lose a reference that belongs to the nsproxy the caller keeps
using:

  WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230
   nsproxy_ns_active_put
   deactivate_nsproxy
   ksys_unshare

Afterwards the namespaces the caller lives in aren't listed by listns()
anymore. set_cred_ucounts() only fails when alloc_ucounts() can't
allocate and it only allocates when the real uid of the caller differs
from its effective uid.

Commit cefd55bd2159 ("nsproxy: fix free_nsproxy() and simplify
create_new_namespaces()") separated the two cases on purpose.
nsproxy_free() frees an nsproxy that was prepared but never installed
and that's what a failed setns() uses in put_nsset(). Export it and use
it for a failed unshare() as well.

## Which versions are affected by CVE-2026-98983?


## How do I fix CVE-2026-98983?

Upgrade to a fixed version.

## Is CVE-2026-98983 being exploited?

There is no known exploitation of CVE-2026-98983 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98983 and fix it if it is affected.

What it is: CVE-2026-98983 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98983 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-2026-98983/ (Markdown: https://insights.sbomify.com/CVE-2026-98983/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98983
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98983
- OSV: https://osv.dev/vulnerability/CVE-2026-98983

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98983/
Summaries are generated and may contain mistakes; the official description above is the record.