# CVE-2026-80731: net: remove CAP_SYS_RAWIO zero-padding in dev_validate_header

> A race condition in the Linux kernel allows out-of-bounds writes via CAP_SYS_RAWIO, potentially enabling code execution or privilege escalation.

- **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:** 3 Sep 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-99054, BELL-CVE-2026-80731, DEBIAN-CVE-2026-80731, GHSA-534x-f2qc-fghv, UBUNTU-CVE-2026-80731

## What is CVE-2026-80731?

CVE-2026-80731 is a high-severity memory corruption vulnerability in Linux, published on 3 Sep 2026. 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:

net: remove CAP_SYS_RAWIO zero-padding in dev_validate_header

dev_validate_header() reads dev->hard_header_len directly when
zero-padding short link layer headers for CAP_SYS_RAWIO holders:

    if (capable(CAP_SYS_RAWIO)) {
        memset(ll_header + len, 0, dev->hard_header_len - len);
        return true;
    }

Packet send paths call dev_validate_header() on skbs whose headroom was
allocated from an earlier hard_header_len read. If the device is
reconfigured so that dev->hard_header_len increases before validation,
the memset writes past the reserved buffer, an out-of-bounds write.

This out-of-bounds write is masked in some SOCK_RAW paths today because
the same concurrent increase can first make skb_push() exceed the
reserved headroom and trigger skb_under_panic(). Remove the zero-padding
branch before making those hard_header_len reads consistent, so the
snapshot fixes do not turn a loud panic into a silent overwrite.

This path is only reached for variable length L2 protocols, where
len < hard_header_len but len >= min_header_len. No remaining in-tree
variable length L2 protocol implements header_ops->validate, and the
CAP_SYS_RAWIO bypass that zero-pads and accepts short headers has no
real value beyond allowing testing of intentionally malformed input.

Drop the CAP_SYS_RAWIO branch. The remaining reads of
dev->hard_header_len in dev_validate_header() are comparisons only and
have no memory safety impact.

## Which versions are affected by CVE-2026-80731?


## How do I fix CVE-2026-80731?

Apply the vendor's patch.

## Is CVE-2026-80731 being exploited?

There is no known exploitation of CVE-2026-80731 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80731 and fix it if it is affected.

What it is: CVE-2026-80731 is a high-severity memory corruption vulnerability in Linux, published on 3 Sep 2026. 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-2026-80731 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-2026-80731/ (Markdown: https://insights.sbomify.com/CVE-2026-80731/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80731
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80731
- OSV: https://osv.dev/vulnerability/CVE-2026-80731

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80731/
Summaries are generated and may contain mistakes; the official description above is the record.