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

{
  "id": "0cb10b8e26d4886bae12c2707de7a62e6f9aac9a1008880e60bac5ddb0eccdbb",
  "url": "https://osv.dev/vulnerability/CVE-2026-23439",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "udp_tunnel: fix NULL deref caused by udp_sock_create6 when CONFIG_IPV6=n",
    "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 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: 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",
    "evidence": "osv:CVE-2026-23439",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.253",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.203",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.167",
            "evidence": "/affected/1/ranges"
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          {
            "value": "6.6.130",
            "evidence": "/affected/1/ranges"
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          {
            "value": "6.12.78",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.20",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.10",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-23439",
      "aliases": [
        "CVE-2026-23439"
      ],
      "affected": [
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                {
                  "fixed": "66117dbb3dbae82f86735bf727b1d59cc677afa1"
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                {
                  "fixed": "ba7c9ddcdd077942b798979edb035207374d4096"
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                  "fixed": "a05a2149386f6dfb4245f522acdbef892acafc84"
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23439.json"
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23439.json"
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      ],
      "modified": "2026-10-28T02:30:33.410091245Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://git.kernel.org/stable/c/003343985f26dfefd0c94b1fe1316a2de74428b9",
        "https://git.kernel.org/stable/c/12aa4b73a67d95bc739995a2d6943aec2f9785c9",
        "https://git.kernel.org/stable/c/66117dbb3dbae82f86735bf727b1d59cc677afa1",
        "https://git.kernel.org/stable/c/9f036aa0fe46c19e938f03d10e02c23f4fffae5e",
        "https://git.kernel.org/stable/c/a05a2149386f6dfb4245f522acdbef892acafc84",
        "https://git.kernel.org/stable/c/b3a6df291fecf5f8a308953b65ca72b7fc9e015d",
        "https://git.kernel.org/stable/c/ba7c9ddcdd077942b798979edb035207374d4096",
        "https://git.kernel.org/stable/c/dfc96ae0074cc47b5478a59e5aa19233e434243f",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23439.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23439",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23439.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-23439",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 500273,
  "published_at": "2026-04-03T15:15:23.734+00:00"
}