# CVE-2021-47517: ethtool: do not perform operations on net devices being unregistered

> A race condition in the Linux kernel ethtool netlink interface allows use-after-free, potentially leading to code execution or system crash.

- **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:** 24 May 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-47517, UBUNTU-CVE-2021-47517

## What is CVE-2021-47517?

CVE-2021-47517 is a high-severity use after free vulnerability in Linux kernel, published on 24 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:

ethtool: do not perform operations on net devices being unregistered

There is a short period between a net device starts to be unregistered
and when it is actually gone. In that time frame ethtool operations
could still be performed, which might end up in unwanted or undefined
behaviours[1].

Do not allow ethtool operations after a net device starts its
unregistration. This patch targets the netlink part as the ioctl one
isn't affected: the reference to the net device is taken and the
operation is executed within an rtnl lock section and the net device
won't be found after unregister.

[1] For example adding Tx queues after unregister ends up in NULL
    pointer exceptions and UaFs, such as:

      BUG: KASAN: use-after-free in kobject_get+0x14/0x90
      Read of size 1 at addr ffff88801961248c by task ethtool/755

      CPU: 0 PID: 755 Comm: ethtool Not tainted 5.15.0-rc6+ #778
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/014
      Call Trace:
       dump_stack_lvl+0x57/0x72
       print_address_description.constprop.0+0x1f/0x140
       kasan_report.cold+0x7f/0x11b
       kobject_get+0x14/0x90
       kobject_add_internal+0x3d1/0x450
       kobject_init_and_add+0xba/0xf0
       netdev_queue_update_kobjects+0xcf/0x200
       netif_set_real_num_tx_queues+0xb4/0x310
       veth_set_channels+0x1c3/0x550
       ethnl_set_channels+0x524/0x610

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-47517?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47517?

Apply the vendor's patch.

## Is CVE-2021-47517 being exploited?

There is no known exploitation of CVE-2021-47517 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-2021-47517 and fix it if it is affected.

What it is: CVE-2021-47517 is a high-severity use after free vulnerability in Linux kernel, published on 24 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-2021-47517 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-2021-47517/ (Markdown: https://insights.sbomify.com/CVE-2021-47517/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47517
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47517
- OSV: https://osv.dev/vulnerability/CVE-2021-47517

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47517/
Summaries are generated and may contain mistakes; the official description above is the record.