VDB-327700 · CVE-2025-39955 · Nessus 272003

Linux Kernel up to 6.16.8 net/ipv4/tcp_timer.c tcp_disconnect denial of service

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6.4	$0-$5k	0.00

Summaryinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 6.16.8. Affected is the function tcp_disconnect of the file net/ipv4/tcp_timer.c. Executing a manipulation can lead to denial of service. This vulnerability is registered as CVE-2025-39955. It is possible to launch the attack remotely. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in Linux Kernel up to 6.16.8. This vulnerability affects the function tcp_disconnect of the file net/ipv4/tcp_timer.c. The manipulation with an unknown input leads to a denial of service vulnerability. The CWE definition for the vulnerability is CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. As an impact it is known to affect availability. CVE summarizes:

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>

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2025-39955 since 04/16/2025. The exploitation appears to be difficult. The attack can be initiated remotely. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

The vulnerability scanner Nessus provides a plugin with the ID 272003 (CentOS 9 : kernel-5.14.0-631.el9), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.4.300, 5.10.245, 5.15.194, 6.1.154, 6.6.108, 6.12.49 or 6.16.9 eliminates this vulnerability. Applying the patch 7ec092a91ff351dcde89c23e795b73a328274db6/a4378dedd6e07e62f2fccb17d78c9665718763d0/33a4fdf0b4a25f8ce65380c3b0136b407ca57609/17d699727577814198d744d6afe54735c6b54c99/dfd06131107e7b699ef1e2a24ed2f7d17c917753/fa4749c065644af4db496b338452a69a3e5147d9/ae313d14b45eca7a6bb29cb9bf396d977e7d28fb/45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (272003) and CERT Bund (WID-SEC-2025-2246). Once again VulDB remains the best source for vulnerability data.

Affected

Debian Linux
Amazon Linux 2
Red Hat Enterprise Linux
Ubuntu Linux
SUSE Linux
Oracle Linux
SUSE openSUSE
RESF Rocky Linux
Open Source Linux Kernel
IBM QRadar SIEM

Productinfo

Type

Operating System

Vendor

Linux

Name

Kernel

Version

License

open-source

Website

Vendor: https://www.kernel.org/

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.5
VulDB Meta Temp Score: 6.4

VulDB Base Score: 5.3
VulDB Temp Score: 5.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 7.8
NVD Vector: 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Denial of service
CWE: CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 272003
Nessus Name: CentOS 9 : kernel-5.14.0-631.el9

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Timelineinfo

04/16/2025 CVE reserved
10/09/2025 +176 days Advisory disclosed
10/09/2025 +0 days VulDB entry created
02/13/2026 +127 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-39955 (🔒)
GCVE (CVE): GCVE-0-2025-39955
GCVE (VulDB): GCVE-100-327700
CERT Bund: WID-SEC-2025-2246 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 10/09/2025 12:48
Updated: 02/13/2026 03:21
Changes: 10/09/2025 12:48 (59), 10/09/2025 13:35 (7), 10/30/2025 12:23 (2), 11/21/2025 04:51 (1), 11/25/2025 11:04 (1), 11/30/2025 14:26 (1), 12/22/2025 04:02 (1), 02/03/2026 18:00 (12), 02/13/2026 03:21 (1)
Complete: 🔍
Cache ID: 216::103