# CVE-2026-97971: nstree: check listing permission before taking a namespace reference

> A race condition in the Linux kernel namespace listing allows a local attacker to trigger a kernel warning and potential denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-97971, GHSA-7r96-j35v-9x4x, UBUNTU-CVE-2026-97971

## What is CVE-2026-97971?

CVE-2026-97971 is a high-severity vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

nstree: check listing permission before taking a namespace reference

legitimize_ns() takes a reference on the candidate namespace before
may_list_ns() has decided whether the caller may see it. The
__free(ns_put) cleanup on the denied path can drop the last reference to a
mount namespace while we still hold the rcu read lock, and put_mnt_ns()
may sleep there. This is the same problem commit 2ec2aff3c8e2 ("ns: make
sure reference are dropped outside of rcu lock") fixed for the put_user()
path. Neither ns_requested() nor may_list_ns() needs a reference, both
only look at the namespace type and at the caller's own namespaces, so do
the checks first and take the reference last.

Splat:

  Voluntary context switch within RCU read-side critical section!
  WARNING: kernel/rcu/tree_plugin.h:332 at rcu_note_context_switch+0x238/0x2a0, CPU#5: a/3442
  CPU: 5 UID: 1000 PID: 3442 Comm: a Not tainted 7.0.0-30-generic #30-Ubuntu PREEMPT(lazy)
  RIP: 0010:rcu_note_context_switch+0x238/0x2a0
  Call Trace:
   <TASK>
   __schedule+0xcf/0x650
   schedule+0x27/0x90
   schedule_preempt_disabled+0x15/0x30
   __mutex_lock.constprop.0+0x550/0xaf0
   __mutex_lock_slowpath+0x13/0x20
   mutex_lock+0x3b/0x50
   exp_funnel_lock+0xb2/0x260
   synchronize_rcu_expedited+0xe7/0x220
   namespace_unlock+0x26a/0x320
   put_mnt_ns+0xd3/0x120
   mntns_put+0xe/0x20
   do_listns+0x13e/0x560
   __do_sys_listns+0x126/0x2d0
   __x64_sys_listns+0x20/0x30
   x64_sys_call+0x2366/0x2390
   do_syscall_64+0x105/0x5a0
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
   </TASK>

## Which versions are affected by CVE-2026-97971?


## How do I fix CVE-2026-97971?

Apply the vendor's patch.

## Is CVE-2026-97971 being exploited?

There is no known exploitation of CVE-2026-97971 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97971 and fix it if it is affected.

What it is: CVE-2026-97971 is a high-severity vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-97971 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-2026-97971/ (Markdown: https://insights.sbomify.com/CVE-2026-97971/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97971
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97971
- OSV: https://osv.dev/vulnerability/CVE-2026-97971

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97971/
Summaries are generated and may contain mistakes; the official description above is the record.