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

Affected: Linux, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

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 RD…

USN-8033-1 — linux, linux-aws, linux-gcp, linux-gke, linux-gkeop, linux-hwe-5.15, linux-ibm, linux-ibm-5.15, linux-lowlatency, linux…

Affected: Ubuntu:Pro:20.04:LTS: linux-hwe-5.15, Ubuntu:Pro:20.04:LTS: linux-ibm-5.15, Ubuntu:Pro:20.04:LTS: linux-lowlatency-hwe-5.15, Ubuntu:22.04:LTS: linux, Ubuntu:22.04:LTS: linux-aws, Ubuntu:22.04:LTS: linux-gcp, Ubuntu:22.04:LTS: linux-gke, Ubuntu:22.04:LTS: linux-gkeop, Ubuntu:22.04:LTS: linux-ibm, Ubuntu:22.04:LTS: linux-lowlatency

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - Nios II architecture; - Sun Sparc architecture; - User-Mode Linux (UML); - x86 architecture; - Block layer subsystem; - Cryptographic API; - Drivers core; - Bus devices; - Hardware random number generator core; - Data acquisition framework and drivers; - CPU frequency scaling framework; - DMA engine subsystem; - GPU drivers; - HW tracing; - Input Device (Miscellaneous) drivers; - Multiple devices driver; - Media drivers; - MOST (Media Oriented Systems Transport) drivers; - MTD block device drivers; - Network drivers; - NVME drivers; - PCI subsystem; - Performance monitor drivers; - Pin controllers subsystem; - x86 platform drivers; - PPS (Pulse Per Second) driver; - PWM drivers; - SCSI subsystem; - TCM subsystem; - Userspace I/O drivers; - USB Gadget drivers; - USB Host Controller drivers; - Framebuffer layer; - BTRFS file system; - File systems infrastructure; - Ext4 file system; - Network file system (NFS) server daemon; - NTFS3 file system; - SMB network file system; - padata parallel execution mechanism; - IP tunnels definitions; - Network sockets; - XFRM subsystem; - Control group (cgroup); - Padata parallel execution mechanism; - PID allocator; - Tracing infrastructure; - Memory management; - 9…

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

USN-8033-1 — linux, linux-aws, linux-gcp, linux-gke, linux-gkeop, linux-hwe-5.15, linux-ibm, linux-ibm-5.15, linux-lowlatency, linux…