CVE-2025-40186 (GCVE-0-2025-40186)

Vulnerability from cvelistv5 – Published: 2025-11-12 21:56 – Updated: 2026-10-15 22:02
VLAI
Title
tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().
Summary
In the Linux kernel, the following vulnerability has been resolved: tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request(). syzbot reported the splat below in tcp_conn_request(). [0] If a listener is close()d while a TFO socket is being processed in tcp_conn_request(), inet_csk_reqsk_queue_add() does not set reqsk->sk and calls inet_child_forget(), which calls tcp_disconnect() for the TFO socket. After the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(), where reqsk_put() is called due to !reqsk->sk. Then, reqsk_fastopen_remove() in tcp_conn_request() decrements the last req->rsk_refcnt and frees reqsk, and __reqsk_free() at the drop_and_free label causes the refcount underflow for the listener and double-free of the reqsk. Let's remove reqsk_fastopen_remove() in tcp_conn_request(). Note that other callers make sure tp->fastopen_rsk is not NULL. [0]: refcount_t: underflow; use-after-free. WARNING: CPU: 12 PID: 5563 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28) Modules linked in: CPU: 12 UID: 0 PID: 5563 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:refcount_warn_saturate (lib/refcount.c:28) Code: 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 RSP: 0018:ffffa79fc0304a98 EFLAGS: 00010246 RAX: d83af4db1c6b3900 RBX: ffff9f65c7a69020 RCX: d83af4db1c6b3900 RDX: 0000000000000000 RSI: 00000000ffff7fff RDI: ffffffffac78a280 RBP: 000000009d781b60 R08: 0000000000007fff R09: ffffffffac6ca280 R10: 0000000000017ffd R11: 0000000000000004 R12: ffff9f65c7b4f100 R13: ffff9f65c7d23c00 R14: ffff9f65c7d26000 R15: ffff9f65c7a64ef8 FS: 00007f9f962176c0(0000) GS:ffff9f65fcf00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000180 CR3: 000000000dbbe006 CR4: 0000000000372ef0 Call Trace: <IRQ> tcp_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) tcp_rcv_state_process (net/ipv4/tcp_input.c:6708) tcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670) tcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906) ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438) ip6_input (net/ipv6/ip6_input.c:500) ipv6_rcv (net/ipv6/ip6_input.c:311) __netif_receive_skb (net/core/dev.c:6104) process_backlog (net/core/dev.c:6456) __napi_poll (net/core/dev.c:7506) net_rx_action (net/core/dev.c:7569 net/core/dev.c:7696) handle_softirqs (kernel/softirq.c:579) do_softirq (kernel/softirq.c:480) </IRQ>
Severity
8.1 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-15 21:57 UTC
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6641 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 7ec092a91ff351dcde89c23e795b73a328274db6 , < e359b742eac1eac75cff4e38ee2e8cea492acd9b (git)
Affected: a4378dedd6e07e62f2fccb17d78c9665718763d0 , < ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d (git)
Affected: 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 , < eb85ad5f23268d64b037bfb545cbcba3752f90c7 (git)
Affected: 17d699727577814198d744d6afe54735c6b54c99 , < 643a94b0cf767325e953591c212be2eb826b9d7f (git)
Affected: dfd06131107e7b699ef1e2a24ed2f7d17c917753 , < 422c1c173c39bbbae1e0eaaf8aefe40b2596233b (git)
Affected: fa4749c065644af4db496b338452a69a3e5147d9 , < c11ace909e873118295e9eb22dc8c58b0b50eb32 (git)
Affected: 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 , < 64dc47a13aa3d9daf7cec29b44dca8e22a6aea15 (git)
Affected: 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 , < 2e7cbbbe3d61c63606994b7ff73c72537afe2e1c (git)
Affected: ae313d14b45eca7a6bb29cb9bf396d977e7d28fb (git)
Affected: 5.4.300 , < 5.4.301 (semver)
Affected: 5.10.245 , < 5.10.246 (semver)
Affected: 5.15.194 , < 5.15.195 (semver)
Affected: 6.1.154 , < 6.1.157 (semver)
Affected: 6.6.108 , < 6.6.113 (semver)
Affected: 6.12.49 , < 6.12.54 (semver)
Affected: 6.16.9 , < 6.17 (semver)
guessed Create a notification for this product.
Linux Linux Affected: 6.17
Unaffected: 0 , < 6.17 (semver)
Unaffected: 5.4.301 , ≤ 5.4.* (semver)
Unaffected: 5.10.246 , ≤ 5.10.* (semver)
Unaffected: 5.15.195 , ≤ 5.15.* (semver)
Unaffected: 6.1.157 , ≤ 6.1.* (semver)
Unaffected: 6.6.113 , ≤ 6.6.* (semver)
Unaffected: 6.12.54 , ≤ 6.12.* (semver)
Unaffected: 6.17.4 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Don\u0027t call reqsk_fastopen_remove() in tcp_conn_request().\n\nsyzbot reported the splat below in tcp_conn_request(). [0]\n\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-\u003esk\nand calls inet_child_forget(), which calls tcp_disconnect() for the\nTFO socket.\n\nAfter the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(),\nwhere reqsk_put() is called due to !reqsk-\u003esk.\n\nThen, reqsk_fastopen_remove() in tcp_conn_request() decrements the\nlast req-\u003ersk_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.\n\nLet\u0027s remove reqsk_fastopen_remove() in tcp_conn_request().\n\nNote that other callers make sure tp-\u003efastopen_rsk is not NULL.\n\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 \u003c0f\u003e 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 \u003cIRQ\u003e\n tcp_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)\n tcp_rcv_state_process (net/ipv4/tcp_input.c:6708)\n tcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670)\n tcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906)\n ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438)\n ip6_input (net/ipv6/ip6_input.c:500)\n ipv6_rcv (net/ipv6/ip6_input.c:311)\n __netif_receive_skb (net/core/dev.c:6104)\n process_backlog (net/core/dev.c:6456)\n __napi_poll (net/core/dev.c:7506)\n net_rx_action (net/core/dev.c:7569 net/core/dev.c:7696)\n handle_softirqs (kernel/softirq.c:579)\n do_softirq (kernel/softirq.c:480)\n \u003c/IRQ\u003e"
        }
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        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
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            {
              "lang": "en",
              "value": "AV:N - The vulnerable code is in the TCP/IP stack\u0027s inbound SYN-processing path (tcp_v6_rcv \u2192 tcp_rcv_state_process \u2192 tcp_conn_request), triggered by a received TCP Fast Open SYN packet from a remote peer.\nAC:H - Triggering requires the listener socket to transition out of TCP_LISTEN (a local close()/shutdown()) at the exact moment an inbound TFO SYN is being processed; a remote attacker cannot control the timing of that close, so success depends on conditions beyond their control.\nPR:N - The TFO SYN is processed pre-connection with no authentication; an unauthenticated remote attacker needs no privileges to reach tcp_conn_request().\nUI:N - The bug is triggered purely by network packet processing racing with a listener close; no victim interaction is required.\nS:U - The corruption stays within the kernel\u0027s own memory/security authority (request_sock slab and listener refcount); no VM/IOMMU/sandbox boundary is crossed.\nC:H - The refcount underflow yields a use-after-free/double-free of a request_sock, giving an attacker control over freed-object contents that can be leveraged to read adjacent kernel memory.\nI:H - The double-free/UAF is a heap-corruption primitive that can be groomed into an arbitrary-write / control-flow-hijack, so integrity impact is high.\nA:H - The refcount underflow and double-free reliably corrupt kernel memory and crash the kernel (oops/panic in softirq context), a high availability impact."
            }
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        }
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      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:08:24.563Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        {
          "url": "https://git.kernel.org/stable/c/e359b742eac1eac75cff4e38ee2e8cea492acd9b"
        },
        {
          "url": "https://git.kernel.org/stable/c/ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d"
        },
        {
          "url": "https://git.kernel.org/stable/c/eb85ad5f23268d64b037bfb545cbcba3752f90c7"
        },
        {
          "url": "https://git.kernel.org/stable/c/643a94b0cf767325e953591c212be2eb826b9d7f"
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        },
        {
          "url": "https://git.kernel.org/stable/c/2e7cbbbe3d61c63606994b7ff73c72537afe2e1c"
        }
      ],
      "title": "tcp: Don\u0027t call reqsk_fastopen_remove() in tcp_conn_request().",
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    "cveId": "CVE-2025-40186",
    "datePublished": "2025-11-12T21:56:29.033Z",
    "dateReserved": "2025-04-16T07:20:57.177Z",
    "dateUpdated": "2026-10-15T22:02:39.982Z",
    "state": "PUBLISHED"
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                  {
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                    "versionType": "git"
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                  {
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                  {
                    "lessThan": "c11ace909e873118295e9eb22dc8c58b0b50eb32",
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                    "version": "fa4749c065644af4db496b338452a69a3e5147d9",
                    "versionType": "git"
                  },
                  {
                    "lessThan": "64dc47a13aa3d9daf7cec29b44dca8e22a6aea15",
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                  {
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                  {
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                    "status": "affected",
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                    "status": "affected",
                    "version": "5.15.194",
                    "versionType": "semver"
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                    "status": "affected",
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                  {
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                    "status": "affected",
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                    "versionType": "semver"
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                  {
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                    "versionType": "semver"
                  },
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                    "status": "affected",
                    "version": "6.16.9",
                    "versionType": "semver"
                  }
                ]
              },
              {
                "defaultStatus": "affected",
                "product": "Linux",
                "programFiles": [
                  "net/ipv4/tcp_input.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
                  {
                    "status": "affected",
                    "version": "6.17"
                  },
                  {
                    "lessThan": "6.17",
                    "status": "unaffected",
                    "version": "0",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "5.4.*",
                    "status": "unaffected",
                    "version": "5.4.301",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "5.10.*",
                    "status": "unaffected",
                    "version": "5.10.246",
                    "versionType": "semver"
                  },
                  {
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                    "status": "unaffected",
                    "version": "5.15.195",
                    "versionType": "semver"
                  },
                  {
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                    "status": "unaffected",
                    "version": "6.1.157",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "6.6.*",
                    "status": "unaffected",
                    "version": "6.6.113",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "6.12.*",
                    "status": "unaffected",
                    "version": "6.12.54",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "6.17.*",
                    "status": "unaffected",
                    "version": "6.17.4",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "*",
                    "status": "unaffected",
                    "version": "6.18",
                    "versionType": "original_commit_for_fix"
                  }
                ]
              }
            ],
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Don\u0027t call reqsk_fastopen_remove() in tcp_conn_request().\n\nsyzbot reported the splat below in tcp_conn_request(). [0]\n\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-\u003esk\nand calls inet_child_forget(), which calls tcp_disconnect() for the\nTFO socket.\n\nAfter the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(),\nwhere reqsk_put() is called due to !reqsk-\u003esk.\n\nThen, reqsk_fastopen_remove() in tcp_conn_request() decrements the\nlast req-\u003ersk_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.\n\nLet\u0027s remove reqsk_fastopen_remove() in tcp_conn_request().\n\nNote that other callers make sure tp-\u003efastopen_rsk is not NULL.\n\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 \u003c0f\u003e 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 \u003cIRQ\u003e\n tcp_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)\n tcp_rcv_state_process (net/ipv4/tcp_input.c:6708)\n tcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670)\n tcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906)\n ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438)\n ip6_input (net/ipv6/ip6_input.c:500)\n ipv6_rcv (net/ipv6/ip6_input.c:311)\n __netif_receive_skb (net/core/dev.c:6104)\n process_backlog (net/core/dev.c:6456)\n __napi_poll (net/core/dev.c:7506)\n net_rx_action (net/core/dev.c:7569 net/core/dev.c:7696)\n handle_softirqs (kernel/softirq.c:579)\n do_softirq (kernel/softirq.c:480)\n \u003c/IRQ\u003e"
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\ntcp: No llamar a reqsk_fastopen_remove() en tcp_conn_request().\n\nsyzbot inform\u00f3 el \u0027splat\u0027 a continuaci\u00f3n en tcp_conn_request(). [0]\n\nSi un \u0027listener\u0027 es cerrado (close()) mientras un socket TFO est\u00e1 siendo procesado en tcp_conn_request(), inet_csk_reqsk_queue_add() no establece reqsk-\u003esk y llama a inet_child_forget(), lo que llama a tcp_disconnect() para el socket TFO.\n\nDespu\u00e9s del \u0027commit\u0027 citado, tcp_disconnect() llama a reqsk_fastopen_remove(), donde se llama a reqsk_put() debido a !reqsk-\u003esk.\n\nLuego, reqsk_fastopen_remove() en tcp_conn_request() decrementa el \u00faltimo req-\u003ersk_refcnt y libera reqsk, y __reqsk_free() en la etiqueta drop_and_free causa el desbordamiento negativo del contador de referencias para el \u0027listener\u0027 y la doble liberaci\u00f3n de reqsk.\n\nEliminemos reqsk_fastopen_remove() en tcp_conn_request().\n\nN\u00f3tese que otros llamadores se aseguran de que tp-\u003efastopen_rsk no sea NULL.\n\n[0]:\nrefcount_t: desbordamiento negativo; uso despu\u00e9s de liberaci\u00f3n.\nADVERTENCIA: CPU: 12 PID: 5563 en lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28)\nM\u00f3dulos enlazados:\nCPU: 12 UID: 0 PID: 5563 Comm: syz-executor No contaminado syzkaller #0 PREEMPT(full)\nNombre del hardware: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025\nRIP: 0010:refcount_warn_saturate (lib/refcount.c:28)\nC\u00f3digo: 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 \u003c0f\u003e 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\nRastro de llamadas:\n \u003cIRQ\u003e\n tcp_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)\n tcp_rcv_state_process (net/ipv4/tcp_input.c:6708)\n tcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670)\n tcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906)\n ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438)\n ip6_input (net/ipv6/ip6_input.c:500)\n ipv6_rcv (net/ipv6/ip6_input.c:311)\n __netif_receive_skb (net/core/dev.c:6104)\n process_backlog (net/core/dev.c:6456)\n __napi_poll (net/core/dev.c:7506)\n net_rx_action (net/core/dev.c:7569 net/core/dev.c:7696)\n handle_softirqs (kernel/softirq.c:579)\n do_softirq (kernel/softirq.c:480)\n \u003c/IRQ\u003e"
          }
        ],
        "id": "CVE-2025-40186",
        "lastModified": "2026-10-19T21:10:00.160",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 8.1,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 2.2,
              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
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                "options": [
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                    "exploitation": "none"
                  },
                  {
                    "automatable": "no"
                  },
                  {
                    "technicalImpact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-15T21:57:46.472825Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2025-11-12T22:15:45.443",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/2e7cbbbe3d61c63606994b7ff73c72537afe2e1c"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/422c1c173c39bbbae1e0eaaf8aefe40b2596233b"
          },
          {
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          },
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            "url": "https://git.kernel.org/stable/c/e359b742eac1eac75cff4e38ee2e8cea492acd9b"
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            "url": "https://git.kernel.org/stable/c/eb85ad5f23268d64b037bfb545cbcba3752f90c7"
          },
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Deferred"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-11-04T21:29:58+00:00",
      "cve": "CVE-2025-40186",
      "id": "CVE-2025-40186",
      "initial_release_date": "2025-11-12T00:00:00+00:00",
      "product_status:fixed": "1392",
      "product_status:known_affected": "121",
      "product_status:known_not_affected": "31",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: Privilege escalation or Denial of Service via TCP Fast Open vulnerability",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-40186.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-11-05T01:32:24Z",
      "cve": "CVE-2025-40186",
      "id": "CVE-2025-40186",
      "initial_release_date": "2025-11-14T00:24:02Z",
      "product_status:known_affected": "396",
      "product_status:known_not_affected": "322",
      "product_status:recommended": "628",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-40186",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2025/cve-2025-40186.json",
      "version": "56"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2025-40186",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "total"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-10-15T21:57:46.472825Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-10-15T21:57:47.283Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "Linux",
              "programFiles": [
                "net/ipv4/tcp_input.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
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                  "versionType": "git"
                },
                {
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                  "versionType": "git"
                },
                {
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                  "versionType": "git"
                },
                {
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                  "versionType": "git"
                },
                {
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                  "versionType": "git"
                },
                {
                  "lessThan": "64dc47a13aa3d9daf7cec29b44dca8e22a6aea15",
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                },
                {
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                  "versionType": "git"
                },
                {
                  "lessThan": "5.4.301",
                  "status": "affected",
                  "version": "5.4.300",
                  "versionType": "semver"
                },
                {
                  "lessThan": "5.10.246",
                  "status": "affected",
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                  "versionType": "semver"
                },
                {
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                  "status": "affected",
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                {
                  "lessThan": "6.1.157",
                  "status": "affected",
                  "version": "6.1.154",
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                },
                {
                  "lessThan": "6.6.113",
                  "status": "affected",
                  "version": "6.6.108",
                  "versionType": "semver"
                },
                {
                  "lessThan": "6.12.54",
                  "status": "affected",
                  "version": "6.12.49",
                  "versionType": "semver"
                },
                {
                  "lessThan": "6.17",
                  "status": "affected",
                  "version": "6.16.9",
                  "versionType": "semver"
                }
              ]
            },
            {
              "defaultStatus": "affected",
              "product": "Linux",
              "programFiles": [
                "net/ipv4/tcp_input.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "status": "affected",
                  "version": "6.17"
                },
                {
                  "lessThan": "6.17",
                  "status": "unaffected",
                  "version": "0",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.4.*",
                  "status": "unaffected",
                  "version": "5.4.301",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.10.*",
                  "status": "unaffected",
                  "version": "5.10.246",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.15.*",
                  "status": "unaffected",
                  "version": "5.15.195",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.1.*",
                  "status": "unaffected",
                  "version": "6.1.157",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.6.*",
                  "status": "unaffected",
                  "version": "6.6.113",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.12.*",
                  "status": "unaffected",
                  "version": "6.12.54",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.17.*",
                  "status": "unaffected",
                  "version": "6.17.4",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "6.18",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.4.301",
                      "versionStartIncluding": "5.4.300",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.10.246",
                      "versionStartIncluding": "5.10.245",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.15.195",
                      "versionStartIncluding": "5.15.194",
                      "vulnerable": true
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                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.1.157",
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                      "vulnerable": true
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                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.6.113",
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                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.12.54",
                      "versionStartIncluding": "6.12.49",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.17.4",
                      "versionStartIncluding": "6.17",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.18",
                      "versionStartIncluding": "6.17",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionStartIncluding": "6.16.9",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Don\u0027t call reqsk_fastopen_remove() in tcp_conn_request().\n\nsyzbot reported the splat below in tcp_conn_request(). [0]\n\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-\u003esk\nand calls inet_child_forget(), which calls tcp_disconnect() for the\nTFO socket.\n\nAfter the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(),\nwhere reqsk_put() is called due to !reqsk-\u003esk.\n\nThen, reqsk_fastopen_remove() in tcp_conn_request() decrements the\nlast req-\u003ersk_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.\n\nLet\u0027s remove reqsk_fastopen_remove() in tcp_conn_request().\n\nNote that other callers make sure tp-\u003efastopen_rsk is not NULL.\n\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 \u003c0f\u003e 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 \u003cIRQ\u003e\n tcp_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)\n tcp_rcv_state_process (net/ipv4/tcp_input.c:6708)\n tcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670)\n tcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906)\n ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438)\n ip6_input (net/ipv6/ip6_input.c:500)\n ipv6_rcv (net/ipv6/ip6_input.c:311)\n __netif_receive_skb (net/core/dev.c:6104)\n process_backlog (net/core/dev.c:6456)\n __napi_poll (net/core/dev.c:7506)\n net_rx_action (net/core/dev.c:7569 net/core/dev.c:7696)\n handle_softirqs (kernel/softirq.c:579)\n do_softirq (kernel/softirq.c:480)\n \u003c/IRQ\u003e"
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "baseScore": 8.1,
                "baseSeverity": "HIGH",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "scenarios": [
                {
                  "lang": "en",
                  "value": "AV:N - The vulnerable code is in the TCP/IP stack\u0027s inbound SYN-processing path (tcp_v6_rcv \u2192 tcp_rcv_state_process \u2192 tcp_conn_request), triggered by a received TCP Fast Open SYN packet from a remote peer.\nAC:H - Triggering requires the listener socket to transition out of TCP_LISTEN (a local close()/shutdown()) at the exact moment an inbound TFO SYN is being processed; a remote attacker cannot control the timing of that close, so success depends on conditions beyond their control.\nPR:N - The TFO SYN is processed pre-connection with no authentication; an unauthenticated remote attacker needs no privileges to reach tcp_conn_request().\nUI:N - The bug is triggered purely by network packet processing racing with a listener close; no victim interaction is required.\nS:U - The corruption stays within the kernel\u0027s own memory/security authority (request_sock slab and listener refcount); no VM/IOMMU/sandbox boundary is crossed.\nC:H - The refcount underflow yields a use-after-free/double-free of a request_sock, giving an attacker control over freed-object contents that can be leveraged to read adjacent kernel memory.\nI:H - The double-free/UAF is a heap-corruption primitive that can be groomed into an arbitrary-write / control-flow-hijack, so integrity impact is high.\nA:H - The refcount underflow and double-free reliably corrupt kernel memory and crash the kernel (oops/panic in softirq context), a high availability impact."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T12:08:24.563Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/e359b742eac1eac75cff4e38ee2e8cea492acd9b"
            },
            {
              "url": "https://git.kernel.org/stable/c/ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d"
            },
            {
              "url": "https://git.kernel.org/stable/c/eb85ad5f23268d64b037bfb545cbcba3752f90c7"
            },
            {
              "url": "https://git.kernel.org/stable/c/643a94b0cf767325e953591c212be2eb826b9d7f"
            },
            {
              "url": "https://git.kernel.org/stable/c/422c1c173c39bbbae1e0eaaf8aefe40b2596233b"
            },
            {
              "url": "https://git.kernel.org/stable/c/c11ace909e873118295e9eb22dc8c58b0b50eb32"
            },
            {
              "url": "https://git.kernel.org/stable/c/64dc47a13aa3d9daf7cec29b44dca8e22a6aea15"
            },
            {
              "url": "https://git.kernel.org/stable/c/2e7cbbbe3d61c63606994b7ff73c72537afe2e1c"
            }
          ],
          "title": "tcp: Don\u0027t call reqsk_fastopen_remove() in tcp_conn_request().",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2025-40186",
        "datePublished": "2025-11-12T21:56:29.033Z",
        "dateReserved": "2025-04-16T07:20:57.177Z",
        "dateUpdated": "2026-10-15T22:02:39.982Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline

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