---
id: CVE-2026-23439
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  udp_tunnel: fix NULL deref caused by udp_sock_create6 when CONFIG_IPV6=n

  When CONFIG_IPV6 is disabled, the udp_sock_create6() function returns 0
  (success) without actu…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  udp_tunnel: fix NULL deref caused by udp_sock_create6 when CONFIG_IPV6=n

  When CONFIG_IPV6 is disabled, the udp_sock_create6() function returns 0
  (success) without actu…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-476
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 3.18.1, < 5.10.253'
  - 'linux_kernel >= 5.11, < 5.15.203'
  - 'linux_kernel >= 5.16, < 6.1.167'
  - 'linux_kernel >= 6.2, < 6.6.130'
  - 'linux_kernel >= 6.7, < 6.12.78'
  - 'linux_kernel >= 6.13, < 6.18.20'
  - 'linux_kernel >= 6.19, < 6.19.10'
  - linux_kernel = 3.18
  - linux_kernel = 7.0
patched:
  - linux_kernel 6.19.10
published: '2026-04-03'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:18:56.773'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-23439'
references:
  - url: 'https://git.kernel.org/stable/c/003343985f26dfefd0c94b1fe1316a2de74428b9'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/12aa4b73a67d95bc739995a2d6943aec2f9785c9'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/66117dbb3dbae82f86735bf727b1d59cc677afa1'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9f036aa0fe46c19e938f03d10e02c23f4fffae5e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a05a2149386f6dfb4245f522acdbef892acafc84'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b3a6df291fecf5f8a308953b65ca72b7fc9e015d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/ba7c9ddcdd077942b798979edb035207374d4096'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/dfc96ae0074cc47b5478a59e5aa19233e434243f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00129
epssPercentile: 0.02502
ingestedAt: '2026-09-08T15:33:26.992Z'
---

## Overview

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

udp_tunnel: fix NULL deref caused by udp_sock_create6 when CONFIG_IPV6=n

When CONFIG_IPV6 is disabled, the udp_sock_create6() function returns 0
(success) without actually creating a socket. Callers such as
fou_create() then proceed to dereference the uninitialized socket
pointer, resulting in a NULL pointer dereference.

The captured NULL deref crash:
  BUG: kernel NULL pointer dereference, address: 0000000000000018
  RIP: 0010:fou_nl_add_doit (net/ipv4/fou_core.c:590 net/ipv4/fou_core.c:764)
  [...]
  Call Trace:
    <TASK>
    genl_family_rcv_msg_doit.constprop.0 (net/netlink/genetlink.c:1114)
    genl_rcv_msg (net/netlink/genetlink.c:1194 net/netlink/genetlink.c:1209)
    [...]
    netlink_rcv_skb (net/netlink/af_netlink.c:2550)
    genl_rcv (net/netlink/genetlink.c:1219)
    netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344)
    netlink_sendmsg (net/netlink/af_netlink.c:1894)
    __sock_sendmsg (net/socket.c:727 (discriminator 1) net/socket.c:742 (discriminator 1))
    __sys_sendto (./include/linux/file.h:62 (discriminator 1) ./include/linux/file.h:83 (discriminator 1) net/socket.c:2183 (discriminator 1))
    __x64_sys_sendto (net/socket.c:2213 (discriminator 1) net/socket.c:2209 (discriminator 1) net/socket.c:2209 (discriminator 1))
    do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1))
    entry_SYSCALL_64_after_hwframe (net/arch/x86/entry/entry_64.S:130)

This patch makes udp_sock_create6 return -EPFNOSUPPORT instead, so
callers correctly take their error paths. There is only one caller of
the vulnerable function and only privileged users can trigger it.

## Affected

- `linux_kernel >= 3.18.1, < 5.10.253`
- `linux_kernel >= 5.11, < 5.15.203`
- `linux_kernel >= 5.16, < 6.1.167`
- `linux_kernel >= 6.2, < 6.6.130`
- `linux_kernel >= 6.7, < 6.12.78`
- `linux_kernel >= 6.13, < 6.18.20`
- `linux_kernel >= 6.19, < 6.19.10`
- `linux_kernel = 3.18`
- `linux_kernel = 7.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.19.10`