{"id":"CVE-2025-40186","title":"tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Don't 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…","severity":"high","cvss":8.1,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 7ec092a91ff351dcde89c23e795b73a328274db6 < e359b742eac1eac75cff4e38ee2e8cea492acd9b","Linux >= a4378dedd6e07e62f2fccb17d78c9665718763d0 < ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d","Linux >= 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 < eb85ad5f23268d64b037bfb545cbcba3752f90c7","Linux >= 17d699727577814198d744d6afe54735c6b54c99 < 643a94b0cf767325e953591c212be2eb826b9d7f","Linux >= dfd06131107e7b699ef1e2a24ed2f7d17c917753 < 422c1c173c39bbbae1e0eaaf8aefe40b2596233b","Linux >= fa4749c065644af4db496b338452a69a3e5147d9 < c11ace909e873118295e9eb22dc8c58b0b50eb32","Linux >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 64dc47a13aa3d9daf7cec29b44dca8e22a6aea15","Linux >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 2e7cbbbe3d61c63606994b7ff73c72537afe2e1c","Linux ae313d14b45eca7a6bb29cb9bf396d977e7d28fb","Linux >= 5.4.300 < 5.4.301","Linux >= 5.10.245 < 5.10.246","Linux >= 5.15.194 < 5.15.195","Linux >= 6.1.154 < 6.1.157","Linux >= 6.6.108 < 6.6.113","Linux >= 6.12.49 < 6.12.54","Linux >= 6.16.9 < 6.17","Linux 6.17"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-15T21:57:46.472825Z"},"published":"2025-11-12","updated":"2026-10-15","sourceUpdated":"2026-10-15T22:02:39.982Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-40186","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"}],"tags":["cve.org"],"epss":0.0058,"epssPercentile":0.46385,"ingestedAt":"2026-10-15T22:48:25.550Z","slug":"CVE-2025-40186","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Don't 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->sk\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->sk.\n\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.\n\nLet's remove reqsk_fastopen_remove() in tcp_conn_request().\n\nNote that other callers make sure tp->fastopen_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 <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>\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 </IRQ>\n\n## Affected\n\n- `Linux >= 7ec092a91ff351dcde89c23e795b73a328274db6 < e359b742eac1eac75cff4e38ee2e8cea492acd9b`\n- `Linux >= a4378dedd6e07e62f2fccb17d78c9665718763d0 < ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d`\n- `Linux >= 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 < eb85ad5f23268d64b037bfb545cbcba3752f90c7`\n- `Linux >= 17d699727577814198d744d6afe54735c6b54c99 < 643a94b0cf767325e953591c212be2eb826b9d7f`\n- `Linux >= dfd06131107e7b699ef1e2a24ed2f7d17c917753 < 422c1c173c39bbbae1e0eaaf8aefe40b2596233b`\n- `Linux >= fa4749c065644af4db496b338452a69a3e5147d9 < c11ace909e873118295e9eb22dc8c58b0b50eb32`\n- `Linux >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 64dc47a13aa3d9daf7cec29b44dca8e22a6aea15`\n- `Linux >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 2e7cbbbe3d61c63606994b7ff73c72537afe2e1c`\n- `Linux ae313d14b45eca7a6bb29cb9bf396d977e7d28fb`\n- `Linux >= 5.4.300 < 5.4.301`\n- `Linux >= 5.10.245 < 5.10.246`\n- `Linux >= 5.15.194 < 5.15.195`\n- `Linux >= 6.1.154 < 6.1.157`\n- `Linux >= 6.6.108 < 6.6.113`\n- `Linux >= 6.12.49 < 6.12.54`\n- `Linux >= 6.16.9 < 6.17`\n- `Linux 6.17`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":44.6,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}