{
  "threat_severity" : "Important",
  "public_date" : "2025-11-12T00:00:00Z",
  "bugzilla" : {
    "description" : "kernel: Linux kernel: Privilege escalation or Denial of Service via TCP Fast Open vulnerability",
    "id" : "2414724",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2414724"
  },
  "cvss3" : {
    "cvss3_base_score" : "7.0",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
    "status" : "verified"
  },
  "cwe" : "CWE-826",
  "details" : [ "In the Linux kernel, the following vulnerability has been resolved:\ntcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().\nsyzbot reported the splat below in tcp_conn_request(). [0]\nIf a listener is close()d while a TFO socket is being processed in\ntcp_conn_request(), inet_csk_reqsk_queue_add() does not set reqsk->sk\nand calls inet_child_forget(), which calls tcp_disconnect() for the\nTFO socket.\nAfter the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(),\nwhere reqsk_put() is called due to !reqsk->sk.\nThen, reqsk_fastopen_remove() in tcp_conn_request() decrements the\nlast req->rsk_refcnt and frees reqsk, and __reqsk_free() at the\ndrop_and_free label causes the refcount underflow for the listener\nand double-free of the reqsk.\nLet's remove reqsk_fastopen_remove() in tcp_conn_request().\nNote that other callers make sure tp->fastopen_rsk is not NULL.\n[0]:\nrefcount_t: underflow; use-after-free.\nWARNING: CPU: 12 PID: 5563 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28)\nModules linked in:\nCPU: 12 UID: 0 PID: 5563 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025\nRIP: 0010:refcount_warn_saturate (lib/refcount.c:28)\nCode: ab e8 8e b4 98 ff 0f 0b c3 cc cc cc cc cc 80 3d a4 e4 d6 01 00 75 9c c6 05 9b e4 d6 01 01 48 c7 c7 e8 df fb ab e8 6a b4 98 ff <0f> 0b e9 03 5b 76 00 cc 80 3d 7d e4 d6 01 00 0f 85 74 ff ff ff c6\nRSP: 0018:ffffa79fc0304a98 EFLAGS: 00010246\nRAX: d83af4db1c6b3900 RBX: ffff9f65c7a69020 RCX: d83af4db1c6b3900\nRDX: 0000000000000000 RSI: 00000000ffff7fff RDI: ffffffffac78a280\nRBP: 000000009d781b60 R08: 0000000000007fff R09: ffffffffac6ca280\nR10: 0000000000017ffd R11: 0000000000000004 R12: ffff9f65c7b4f100\nR13: ffff9f65c7d23c00 R14: ffff9f65c7d26000 R15: ffff9f65c7a64ef8\nFS:  00007f9f962176c0(0000) GS:ffff9f65fcf00000(0000) knlGS:0000000000000000\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 0000200000000180 CR3: 000000000dbbe006 CR4: 0000000000372ef0\nCall Trace:\n<IRQ>\ntcp_conn_request (./include/linux/refcount.h:400 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 ./include/net/sock.h:1965 ./include/net/request_sock.h:131 net/ipv4/tcp_input.c:7301)\ntcp_rcv_state_process (net/ipv4/tcp_input.c:6708)\ntcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670)\ntcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906)\nip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438)\nip6_input (net/ipv6/ip6_input.c:500)\nipv6_rcv (net/ipv6/ip6_input.c:311)\n__netif_receive_skb (net/core/dev.c:6104)\nprocess_backlog (net/core/dev.c:6456)\n__napi_poll (net/core/dev.c:7506)\nnet_rx_action (net/core/dev.c:7569 net/core/dev.c:7696)\nhandle_softirqs (kernel/softirq.c:579)\ndo_softirq (kernel/softirq.c:480)\n</IRQ>", "A flaw was found in the Linux kernel. A local attacker with low privileges could exploit a memory corruption vulnerability, specifically a use-after-free and double-free, within the TCP Fast Open (TFO) socket processing. This occurs when a listener is closed while a TFO socket is being processed in `tcp_conn_request()`. Successful exploitation could lead to a kernel panic, resulting in a Denial of Service (DoS), or potentially allow the attacker to execute arbitrary code with elevated privileges." ],
  "statement" : "This vulnerability is rated Important for Red Hat Enterprise Linux. A local attacker with low privileges can exploit a use-after-free and double-free flaw in the Linux kernel's TCP Fast Open (TFO) implementation. This could lead to a kernel panic, resulting in a Denial of Service, or potentially allow for privilege escalation. This affects Red Hat Enterprise Linux 7, 8, 9 (up to 9.7.z), and 10 (up to 10.1.z).",
  "affected_release" : [ {
    "product_name" : "Red Hat Enterprise Linux 8",
    "release_date" : "2025-12-01T00:00:00Z",
    "advisory" : "RHSA-2025:22387",
    "cpe" : "cpe:/a:redhat:enterprise_linux:8::nfv",
    "package" : "kernel-rt-0:4.18.0-553.87.1.rt7.428.el8_10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "release_date" : "2025-12-01T00:00:00Z",
    "advisory" : "RHSA-2025:22388",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8",
    "package" : "kernel-0:4.18.0-553.87.1.el8_10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.2 Advanced Update Support",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23445",
    "cpe" : "cpe:/o:redhat:rhel_aus:8.2",
    "package" : "kernel-0:4.18.0-193.178.1.el8_2"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23463",
    "cpe" : "cpe:/o:redhat:rhel_aus:8.4",
    "package" : "kernel-0:4.18.0-305.182.1.el8_4"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23463",
    "cpe" : "cpe:/o:redhat:rhel_eus_long_life:8.4",
    "package" : "kernel-0:4.18.0-305.182.1.el8_4"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23425",
    "cpe" : "cpe:/o:redhat:rhel_aus:8.6",
    "package" : "kernel-0:4.18.0-372.173.1.el8_6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.6 Telecommunications Update Service",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23425",
    "cpe" : "cpe:/o:redhat:rhel_tus:8.6",
    "package" : "kernel-0:4.18.0-372.173.1.el8_6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23425",
    "cpe" : "cpe:/o:redhat:rhel_e4s:8.6",
    "package" : "kernel-0:4.18.0-372.173.1.el8_6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.8 Telecommunications Update Service",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23427",
    "cpe" : "cpe:/o:redhat:rhel_tus:8.8",
    "package" : "kernel-0:4.18.0-477.123.1.el8_8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23427",
    "cpe" : "cpe:/o:redhat:rhel_e4s:8.8",
    "package" : "kernel-0:4.18.0-477.123.1.el8_8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23426",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.0",
    "package" : "kernel-0:5.14.0-70.158.1.el9_0"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23424",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.0::nfv",
    "package" : "kernel-rt-0:5.14.0-70.158.1.rt21.230.el9_0"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23423",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.2",
    "package" : "kernel-0:5.14.0-284.150.1.el9_2"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23422",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.2::nfv",
    "package" : "kernel-rt-0:5.14.0-284.150.1.rt14.435.el9_2"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.4 Extended Update Support",
    "release_date" : "2025-12-17T00:00:00Z",
    "advisory" : "RHSA-2025:23450",
    "cpe" : "cpe:/a:redhat:rhel_eus:9.4",
    "package" : "kernel-0:5.14.0-427.103.1.el9_4"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.6 Extended Update Support",
    "release_date" : "2025-12-01T00:00:00Z",
    "advisory" : "RHSA-2025:22392",
    "cpe" : "cpe:/a:redhat:rhel_eus:9.6",
    "package" : "kernel-0:5.14.0-570.69.1.el9_6"
  } ],
  "package_state" : [ {
    "product_name" : "Red Hat Enterprise Linux 10",
    "fix_state" : "Affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 6",
    "fix_state" : "Not affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2025-40186\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-40186\nhttps://lore.kernel.org/linux-cve-announce/2025111244-CVE-2025-40186-b204@gregkh/T" ],
  "name" : "CVE-2025-40186",
  "csaw" : false
}