VulnerabilityPublished 3 Apr 2026Updated 5 Nov 2026

CVE-2026-23439: Linux kernel · udp_tunnel: fix NULL deref caused by udp_sock_create6 when CONFIG_IPV6=n

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · fixed in dfc96ae0074cc47b5478a59e5aa19233e434243f : update Linux kernel when convenient.

Data as of 5 Nov 2026, 23:24 UTC

Severity

Unrated

Rated by Threat Radar · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none

EPSS

0.1% chance of exploitation in 30 days – higher than 2% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-11-05.

Patch

Available – fixed in dfc96ae0074cc47b5478a59e5aa19233e434243f, ba7c9ddcdd077942b798979edb035207374d4096, b3a6df291fecf5f8a308953b65ca72b7fc9e015d +5

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ fd384412e199b62c3ddaabd18dce86d0e164c5b9, < dfc96ae0074cc47b5478a59e5aa19233e434243f	Fixed in dfc96ae0074cc47b5478a59e5aa19233e434243f
LinuxLinux	Affected ≥ fd384412e199b62c3ddaabd18dce86d0e164c5b9, < ba7c9ddcdd077942b798979edb035207374d4096	Fixed in ba7c9ddcdd077942b798979edb035207374d4096
LinuxLinux	Affected ≥ fd384412e199b62c3ddaabd18dce86d0e164c5b9, < b3a6df291fecf5f8a308953b65ca72b7fc9e015d	Fixed in b3a6df291fecf5f8a308953b65ca72b7fc9e015d
LinuxLinux	Affected ≥ fd384412e199b62c3ddaabd18dce86d0e164c5b9, < a05a2149386f6dfb4245f522acdbef892acafc84	Fixed in a05a2149386f6dfb4245f522acdbef892acafc84
LinuxLinux	Affected ≥ fd384412e199b62c3ddaabd18dce86d0e164c5b9, < 003343985f26dfefd0c94b1fe1316a2de74428b9	Fixed in 003343985f26dfefd0c94b1fe1316a2de74428b9
LinuxLinux	Affected ≥ fd384412e199b62c3ddaabd18dce86d0e164c5b9, < 66117dbb3dbae82f86735bf727b1d59cc677afa1	Fixed in 66117dbb3dbae82f86735bf727b1d59cc677afa1

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.

References

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