---
id: "CVE-2026-98570"
kind: "vulnerability"
aliases: ["CVE-2026-98570"]
title: "Linux kernel IPv6 tunnels: out-of-bounds write when forwarding through VLAN"
severity: "high"
cvss: null
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["ipv6", "linux-kernel", "other", "routers", "segment-routing", "vlan"]
not_affected_if: ["no-seg6-ioam6-rpl", "no-vlan-forwarding"]
published_at: "2026-10-18T16:17:09+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:23:14+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98570", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel IPv6 tunnels: out-of-bounds write when forwarding through VLAN

In the Linux kernel, the seg6, ioam6 and rpl lightweight tunnels can write about 64 KB past a packet buffer when traffic is forwarded through a VLAN device with reorder_hdr off. The memory corruption can crash the kernel or potentially be used for code execution.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- unknown

## Fix

- Update to a Linux kernel release that includes the upstream commit fixing dst_dev_overhead() in net/ipv6, as the sources do not name a version

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98570

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

net: ipv6: keep room for the mac header in dst_dev_overhead()

The seg6, ioam6 and rpl lwtunnels size their skb_cow_head() request as
the length they are about to push plus dst_dev_overhead(), then push the
new headers and rebuild the mac header below them with
skb_mac_header_rebuild().  That rebuild needs skb->mac_len of headroom,
but dst_dev_overhead() leaves LL_RESERVED_SPACE() of the egress device,
16 bytes for plain Ethernet.

Where the mac header is longer than that, as it is on ingress through a
VLAN device with reorder_hdr off, the rebuild runs out of room:
skb_set_mac_header(skb, -skb->mac_len) computes a negative offset,
stores it unchecked in the u16 skb->mac_header, and the memmove that
follows writes skb->mac_len bytes about 64 KB past skb->head.
Forwarding plain ping6 traffic through such a device reproduces it on
all five seg6 encapsulation modes and on the rpl and ioam6 inline paths;
skb->mac_header comes back as 65534 on a 704-byte head.

Return the larger of the two.  The helper already returns skb->mac_len
when it has no dst, so this only makes the other branch agree, and it
covers every caller rather than each call site in turn.

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