# CVE-2021-47013: net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send

> A use-after-free vulnerability in the Linux kernel's EMAC driver allows attackers to potentially execute code or cause a denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Feb 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-47013, GHSA-3ch6-f277-559q, UBUNTU-CVE-2021-47013

## What is CVE-2021-47013?

CVE-2021-47013 is a critical use after free vulnerability in Linux kernel, published on 28 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send

In emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..).
If some error happens in emac_tx_fill_tpd(), the skb will be freed via
dev_kfree_skb(skb) in error branch of emac_tx_fill_tpd().
But the freed skb is still used via skb->len by netdev_sent_queue(,skb->len).

As i observed that emac_tx_fill_tpd() haven't modified the value of skb->len,
thus my patch assigns skb->len to 'len' before the possible free and
use 'len' instead of skb->len later.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-47013?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47013?

Apply the vendor's patch.

## Is CVE-2021-47013 being exploited?

There is no known exploitation of CVE-2021-47013 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-2021-47013 and fix it if it is affected.

What it is: CVE-2021-47013 is a critical use after free vulnerability in Linux kernel, published on 28 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-47013 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-2021-47013/ (Markdown: https://insights.sbomify.com/CVE-2021-47013/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47013
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47013
- OSV: https://osv.dev/vulnerability/CVE-2021-47013

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47013/
Summaries are generated and may contain mistakes; the official description above is the record.