# CVE-2025-40337: net: stmmac: Correctly handle Rx checksum offload errors

> The stmmac driver ignored hardware checksum errors, allowing corrupt packets to be treated as valid, potentially leading to data integrity issues.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40337, DEBIAN-CVE-2025-40337, GHSA-4h2c-rg8h-8jqc, ROOT-OS-DEBIAN-11-CVE-2025-40337, ROOT-OS-DEBIAN-12-CVE-2025-40337, ROOT-OS-DEBIAN-13-CVE-2025-40337, ROOT-OS-UBUNTU-2204-CVE-2025-40337, ROOT-OS-UBUNTU-2404-CVE-2025-40337, UBUNTU-CVE-2025-40337

## What is CVE-2025-40337?

CVE-2025-40337 is a high-severity vulnerability in Linux, published on 9 Dec 2025. 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: stmmac: Correctly handle Rx checksum offload errors

The stmmac_rx function would previously set skb->ip_summed to
CHECKSUM_UNNECESSARY if hardware checksum offload (CoE) was enabled
and the packet was of a known IP ethertype.

However, this logic failed to check if the hardware had actually
reported a checksum error. The hardware status, indicating a header or
payload checksum failure, was being ignored at this stage. This could
cause corrupt packets to be passed up the network stack as valid.

This patch corrects the logic by checking the `csum_none` status flag,
which is set when the hardware reports a checksum error. If this flag
is set, skb->ip_summed is now correctly set to CHECKSUM_NONE,
ensuring the kernel's network stack will perform its own validation and
properly handle the corrupt packet.

## Which versions are affected by CVE-2025-40337?


## How do I fix CVE-2025-40337?

Apply the vendor's patch.

## Is CVE-2025-40337 being exploited?

There is no known exploitation of CVE-2025-40337 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40337 and fix it if it is affected.

What it is: CVE-2025-40337 is a high-severity vulnerability in Linux, published on 9 Dec 2025. 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-2025-40337 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-2025-40337/ (Markdown: https://insights.sbomify.com/CVE-2025-40337/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40337
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40337
- OSV: https://osv.dev/vulnerability/CVE-2025-40337

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40337/
Summaries are generated and may contain mistakes; the official description above is the record.