---
id: CVE-2026-31700
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

  In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points
  directly into the mmap'd TX ring buf…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

  In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points
  directly into the mmap'd TX ring buf…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-362
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 4.6, < 6.6.136'
  - 'linux_kernel >= 6.7, < 6.12.84'
  - 'linux_kernel >= 6.13, < 6.18.25'
  - 'linux_kernel >= 6.19, < 7.0.2'
  - linux_kernel = 7.1
patched:
  - linux_kernel 7.0.2
published: '2026-05-01'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T09:17:59.693'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31700'
references:
  - url: 'https://git.kernel.org/stable/c/0f4c9754956b86de158a4af5278c5cf5bda9439e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/1490f82353bdabc09265a74e645b07f05cf4188e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/714aa973da8163925eda7efd49361ccbee21ee46'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00149
epssPercentile: 0.03403
ingestedAt: '2026-09-08T13:33:23.384Z'
---

## Overview

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

net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points
directly into the mmap'd TX ring buffer shared with userspace. The
kernel validates the header via __packet_snd_vnet_parse() but then
re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent
userspace thread can modify the vnet_hdr fields between validation
and use, bypassing all safety checks.

The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr
to a stack-local variable. All other vnet_hdr consumers in the kernel
(tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX
path is the only caller of virtio_net_hdr_to_skb() that reads directly
from user-controlled shared memory.

Fix this by copying vnet_hdr from the mmap'd ring buffer to a
stack-local variable before validation and use, consistent with the
approach used in packet_snd() and all other callers.

## Affected

- `linux_kernel >= 4.6, < 6.6.136`
- `linux_kernel >= 6.7, < 6.12.84`
- `linux_kernel >= 6.13, < 6.18.25`
- `linux_kernel >= 6.19, < 7.0.2`
- `linux_kernel = 7.1`

## Remediation

Upgrade past the affected range:

- `linux_kernel 7.0.2`