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

• Severity: unknown
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-18 · updated 2026-10-30

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.

Affected products

• Linux: from 3.12.18 before 3.13; from 3.13.10 before 3.14 — fixed in 3.13, 3.14

How to fix

Upgrade to a fixed version: Linux 3.13, 3.14. Check the vendor advisory for mitigations.

References

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

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