{"id":"CVE-2025-39955","title":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect().\n\nsyzbot reported the splat below where a socket had tcp_sk(sk)->fastopen_rsk\nin the TCP_ESTABLISHED state","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect().\n\nsyzbot reported the splat below where a socket had tcp_sk(sk)->fastopen_rsk\nin the TCP_ESTABLISHED state. [0]\n…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 3.7, < 5.4.300","linux_kernel >= 5.5, < 5.10.245","linux_kernel >= 5.11, < 5.15.194","linux_kernel >= 5.16, < 6.1.154","linux_kernel >= 6.2, < 6.6.108","linux_kernel >= 6.7, < 6.12.49","linux_kernel >= 6.13, < 6.16.9","linux_kernel = 6.17"],"patched":["linux_kernel 6.16.9"],"published":"2025-10-09","updated":"2026-10-15","sourceUpdated":"2026-10-15T02:18:03.307","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-39955","references":[{"url":"https://git.kernel.org/stable/c/17d699727577814198d744d6afe54735c6b54c99","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/33a4fdf0b4a25f8ce65380c3b0136b407ca57609","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/7ec092a91ff351dcde89c23e795b73a328274db6","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a4378dedd6e07e62f2fccb17d78c9665718763d0","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/ae313d14b45eca7a6bb29cb9bf396d977e7d28fb","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/dfd06131107e7b699ef1e2a24ed2f7d17c917753","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/fa4749c065644af4db496b338452a69a3e5147d9","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-457936.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00161,"epssPercentile":0.05283,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-06-10T20:41:49.740642Z"},"ingestedAt":"2026-09-08T15:33:26.996Z","slug":"CVE-2025-39955","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\ntcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect().\n\nsyzbot reported the splat below where a socket had tcp_sk(sk)->fastopen_rsk\nin the TCP_ESTABLISHED state. [0]\n\nsyzbot reused the server-side TCP Fast Open socket as a new client before\nthe TFO socket completes 3WHS:\n\n  1. accept()\n  2. connect(AF_UNSPEC)\n  3. connect() to another destination\n\nAs of accept(), sk->sk_state is TCP_SYN_RECV, and tcp_disconnect() changes\nit to TCP_CLOSE and makes connect() possible, which restarts timers.\n\nSince tcp_disconnect() forgot to clear tcp_sk(sk)->fastopen_rsk, the\nretransmit timer triggered the warning and the intended packet was not\nretransmitted.\n\nLet's call reqsk_fastopen_remove() in tcp_disconnect().\n\n[0]:\nWARNING: CPU: 2 PID: 0 at net/ipv4/tcp_timer.c:542 tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7))\nModules linked in:\nCPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted 6.17.0-rc5-g201825fb4278 #62 PREEMPT(voluntary)\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014\nRIP: 0010:tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7))\nCode: 41 55 41 54 55 53 48 8b af b8 08 00 00 48 89 fb 48 85 ed 0f 84 55 01 00 00 0f b6 47 12 3c 03 74 0c 0f b6 47 12 3c 04 74 04 90 <0f> 0b 90 48 8b 85 c0 00 00 00 48 89 ef 48 8b 40 30 e8 6a 4f 06 3e\nRSP: 0018:ffffc900002f8d40 EFLAGS: 00010293\nRAX: 0000000000000002 RBX: ffff888106911400 RCX: 0000000000000017\nRDX: 0000000002517619 RSI: ffffffff83764080 RDI: ffff888106911400\nRBP: ffff888106d5c000 R08: 0000000000000001 R09: ffffc900002f8de8\nR10: 00000000000000c2 R11: ffffc900002f8ff8 R12: ffff888106911540\nR13: ffff888106911480 R14: ffff888106911840 R15: ffffc900002f8de0\nFS:  0000000000000000(0000) GS:ffff88907b768000(0000) knlGS:0000000000000000\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 00007f8044d69d90 CR3: 0000000002c30003 CR4: 0000000000370ef0\nCall Trace:\n <IRQ>\n tcp_write_timer (net/ipv4/tcp_timer.c:738)\n call_timer_fn (kernel/time/timer.c:1747)\n __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2372)\n timer_expire_remote (kernel/time/timer.c:2385 kernel/time/timer.c:2376 kernel/time/timer.c:2135)\n tmigr_handle_remote_up (kernel/time/timer_migration.c:944 kernel/time/timer_migration.c:1035)\n __walk_groups.isra.0 (kernel/time/timer_migration.c:533 (discriminator 1))\n tmigr_handle_remote (kernel/time/timer_migration.c:1096)\n handle_softirqs (./arch/x86/include/asm/jump_label.h:36 ./include/trace/events/irq.h:142 kernel/softirq.c:580)\n irq_exit_rcu (kernel/softirq.c:614 kernel/softirq.c:453 kernel/softirq.c:680 kernel/softirq.c:696)\n sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1050 (discriminator 35) arch/x86/kernel/apic/apic.c:1050 (discriminator 35))\n </IRQ>\n\n## Affected\n\n- `linux_kernel >= 3.7, < 5.4.300`\n- `linux_kernel >= 5.5, < 5.10.245`\n- `linux_kernel >= 5.11, < 5.15.194`\n- `linux_kernel >= 5.16, < 6.1.154`\n- `linux_kernel >= 6.2, < 6.6.108`\n- `linux_kernel >= 6.7, < 6.12.49`\n- `linux_kernel >= 6.13, < 6.16.9`\n- `linux_kernel = 6.17`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.16.9`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":221565,"id":"CVE-2025-39955","ts":1792035263761,"field":"cvss","old":null,"new":"7.8"},{"seq":221564,"id":"CVE-2025-39955","ts":1792035263761,"field":"severity","old":"none","new":"high"}]}