# CVE-2021-47452: netfilter: nf_tables: skip netdev events generated on netns removal

> A race condition in Linux kernel netfilter handling during network namespace removal can trigger a kernel warning, potentially leading to system instability or denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 22 May 2024
- **Updated:** 23 May 2026
- **Also known as:** DEBIAN-CVE-2021-47452, GHSA-hxw5-pvw5-67pp, ROOT-OS-DEBIAN-11-CVE-2021-47452, UBUNTU-CVE-2021-47452

## What is CVE-2021-47452?

CVE-2021-47452 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 May 2024. 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:

netfilter: nf_tables: skip netdev events generated on netns removal

syzbot reported following (harmless) WARN:

 WARNING: CPU: 1 PID: 2648 at net/netfilter/core.c:468
  nft_netdev_unregister_hooks net/netfilter/nf_tables_api.c:230 [inline]
  nf_tables_unregister_hook include/net/netfilter/nf_tables.h:1090 [inline]
  __nft_release_basechain+0x138/0x640 net/netfilter/nf_tables_api.c:9524
  nft_netdev_event net/netfilter/nft_chain_filter.c:351 [inline]
  nf_tables_netdev_event+0x521/0x8a0 net/netfilter/nft_chain_filter.c:382

reproducer:
unshare -n bash -c 'ip link add br0 type bridge; nft add table netdev t ; \
 nft add chain netdev t ingress \{ type filter hook ingress device "br0" \
 priority 0\; policy drop\; \}'

Problem is that when netns device exit hooks create the UNREGISTER
event, the .pre_exit hook for nf_tables core has already removed the
base hook.  Notifier attempts to do this again.

The need to do base hook unregister unconditionally was needed in the past,
because notifier was last stage where reg->dev dereference was safe.

Now that nf_tables does the hook removal in .pre_exit, this isn't
needed anymore.

## Which versions are affected by CVE-2021-47452?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47452?

Apply the vendor's patch.

## Is CVE-2021-47452 being exploited?

There is no known exploitation of CVE-2021-47452 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-2021-47452 and fix it if it is affected.

What it is: CVE-2021-47452 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 May 2024. 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-2021-47452 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-2021-47452/ (Markdown: https://insights.sbomify.com/CVE-2021-47452/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47452
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47452
- OSV: https://osv.dev/vulnerability/CVE-2021-47452

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47452/
Summaries are generated and may contain mistakes; the official description above is the record.