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CVE-2025-39955— tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect().

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于tcp_disconnect未清除tcp_sk(sk)->fastopen_rsk，可能导致数据包未重传。

AI Predicted 4.7 Difficulty: Moderate EPSS 0.16% · P5

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 8336886f786fdacbc19b719c1f7ea91eb70706d4< 7ec092a91ff351dcde89c23e795b73a328274db6 affected
8336886f786fdacbc19b719c1f7ea91eb70706d4< a4378dedd6e07e62f2fccb17d78c9665718763d0 affected
8336886f786fdacbc19b719c1f7ea91eb70706d4< 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 affected
8336886f786fdacbc19b719c1f7ea91eb70706d4< 17d699727577814198d744d6afe54735c6b54c99 affected
8336886f786fdacbc19b719c1f7ea91eb70706d4< dfd06131107e7b699ef1e2a24ed2f7d17c917753 affected
8336886f786fdacbc19b719c1f7ea91eb70706d4< fa4749c065644af4db496b338452a69a3e5147d9 affected
8336886f786fdacbc19b719c1f7ea91eb70706d4< ae313d14b45eca7a6bb29cb9bf396d977e7d28fb affected
8336886f786fdacbc19b719c1f7ea91eb70706d4< 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 affected
… +10 more rows
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I. Basic Information for CVE-2025-39955

Vulnerability Information
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Vulnerability Title
tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect().
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect(). syzbot reported the splat below where a socket had tcp_sk(sk)->fastopen_rsk in the TCP_ESTABLISHED state. [0] syzbot reused the server-side TCP Fast Open socket as a new client before the TFO socket completes 3WHS: 1. accept() 2. connect(AF_UNSPEC) 3. connect() to another destination As of accept(), sk->sk_state is TCP_SYN_RECV, and tcp_disconnect() changes it to TCP_CLOSE and makes connect() possible, which restarts timers. Since tcp_disconnect() forgot to clear tcp_sk(sk)->fastopen_rsk, the retransmit timer triggered the warning and the intended packet was not retransmitted. Let's call reqsk_fastopen_remove() in tcp_disconnect(). [0]: WARNING: CPU: 2 PID: 0 at net/ipv4/tcp_timer.c:542 tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7)) Modules linked in: CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted 6.17.0-rc5-g201825fb4278 #62 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7)) Code: 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 RSP: 0018:ffffc900002f8d40 EFLAGS: 00010293 RAX: 0000000000000002 RBX: ffff888106911400 RCX: 0000000000000017 RDX: 0000000002517619 RSI: ffffffff83764080 RDI: ffff888106911400 RBP: ffff888106d5c000 R08: 0000000000000001 R09: ffffc900002f8de8 R10: 00000000000000c2 R11: ffffc900002f8ff8 R12: ffff888106911540 R13: ffff888106911480 R14: ffff888106911840 R15: ffffc900002f8de0 FS: 0000000000000000(0000) GS:ffff88907b768000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8044d69d90 CR3: 0000000002c30003 CR4: 0000000000370ef0 Call Trace: <IRQ> tcp_write_timer (net/ipv4/tcp_timer.c:738) call_timer_fn (kernel/time/timer.c:1747) __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2372) timer_expire_remote (kernel/time/timer.c:2385 kernel/time/timer.c:2376 kernel/time/timer.c:2135) tmigr_handle_remote_up (kernel/time/timer_migration.c:944 kernel/time/timer_migration.c:1035) __walk_groups.isra.0 (kernel/time/timer_migration.c:533 (discriminator 1)) tmigr_handle_remote (kernel/time/timer_migration.c:1096) handle_softirqs (./arch/x86/include/asm/jump_label.h:36 ./include/trace/events/irq.h:142 kernel/softirq.c:580) irq_exit_rcu (kernel/softirq.c:614 kernel/softirq.c:453 kernel/softirq.c:680 kernel/softirq.c:696) sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1050 (discriminator 35) arch/x86/kernel/apic/apic.c:1050 (discriminator 35)) </IRQ>
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于tcp_disconnect未清除tcp_sk(sk)->fastopen_rsk，可能导致数据包未重传。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 8336886f786fdacbc19b719c1f7ea91eb70706d4 ~ 7ec092a91ff351dcde89c23e795b73a328274db6 -
Linux Linux 3.7 -

II. Public POCs for CVE-2025-39955

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III. Intelligence Information for CVE-2025-39955

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Patches & Fixes for CVE-2025-39955 (1)

Same Patch Batch · Linux · 2025-10-09 · 10 CVEs total

CVE-2025-39961 8.8 HIGH iommu/amd/pgtbl: Fix possible race while increase page table level
CVE-2025-39963 7.8 HIGH io_uring: fix incorrect io_kiocb reference in io_link_skb
CVE-2025-39956 7.8 HIGH igc: don't fail igc_probe() on LED setup error
CVE-2025-39962 7.5 HIGH rxrpc: Fix untrusted unsigned subtract
CVE-2025-39960 7.3 HIGH gpiolib: acpi: initialize acpi_gpio_info struct
CVE-2025-39957 7.1 HIGH wifi: mac80211: increase scan_ies_len for S1G
CVE-2025-39959 ASoC: amd: acp: Fix incorrect retrival of acp_chip_info
CVE-2025-39958 iommu/s390: Make attach succeed when the device was surprise removed
CVE-2025-39954 clk: sunxi-ng: mp: Fix dual-divider clock rate readback

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2025-39955

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