# CVE-2026-31403: NFSD: Hold net reference for the lifetime of /proc/fs/nfs/exports fd

> A use-after-free vulnerability in the Linux kernel NFSD module allows attackers to cause denial of service or execute code via race conditions during network namespace teardown.

- **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:** 3 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-31403, DEBIAN-CVE-2026-31403, GHSA-85m5-f4f3-q6f5, ROOT-OS-DEBIAN-11-CVE-2026-31403, ROOT-OS-DEBIAN-12-CVE-2026-31403, ROOT-OS-DEBIAN-13-CVE-2026-31403, ROOT-OS-UBUNTU-2204-CVE-2026-31403, ROOT-OS-UBUNTU-2404-CVE-2026-31403, UBUNTU-CVE-2026-31403

## What is CVE-2026-31403?

CVE-2026-31403 is a high-severity use after free vulnerability in Linux kernel, published on 3 Apr 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:

NFSD: Hold net reference for the lifetime of /proc/fs/nfs/exports fd

The /proc/fs/nfs/exports proc entry is created at module init
and persists for the module's lifetime. exports_proc_open()
captures the caller's current network namespace and stores
its svc_export_cache in seq->private, but takes no reference
on the namespace. If the namespace is subsequently torn down
(e.g. container destruction after the opener does setns() to a
different namespace), nfsd_net_exit() calls nfsd_export_shutdown()
which frees the cache. Subsequent reads on the still-open fd
dereference the freed cache_detail, walking a freed hash table.

Hold a reference on the struct net for the lifetime of the open
file descriptor. This prevents nfsd_net_exit() from running --
and thus prevents nfsd_export_shutdown() from freeing the cache
-- while any exports fd is open. cache_detail already stores
its net pointer (cd->net, set by cache_create_net()), so
exports_release() can retrieve it without additional per-file
storage.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-31403?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31403?

Apply the vendor's patch.

## Is CVE-2026-31403 being exploited?

There is no known exploitation of CVE-2026-31403 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31403 and fix it if it is affected.

What it is: CVE-2026-31403 is a high-severity use after free vulnerability in Linux kernel, published on 3 Apr 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-2026-31403 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31403/ (Markdown: https://insights.sbomify.com/CVE-2026-31403/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31403
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31403
- OSV: https://osv.dev/vulnerability/CVE-2026-31403

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31403/
Summaries are generated and may contain mistakes; the official description above is the record.