---
id: CVE-2025-38491
title: |-
In the Linux kernel, the following vulnerability has been resolved:
mptcp: make fallback action and fallback decision atomic
Syzkaller reported the following splat:
WARNING: CPU: 1 PID: 7704 at net/mptcp/protocol.h:1223 __mptcp_do_f…
summary: |-
In the Linux kernel, the following vulnerability has been resolved:
mptcp: make fallback action and fallback decision atomic
Syzkaller reported the following splat:
WARNING: CPU: 1 PID: 7704 at net/mptcp/protocol.h:1223 __mptcp_do_f…
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H'
cwe:
- CWE-667
vendor: linux
product: linux_kernel
affected:
- 'linux_kernel >= 5.10.228, < 5.11'
- 'linux_kernel >= 5.15.169, < 5.16'
- 'linux_kernel >= 5.19, < 6.1.149'
- 'linux_kernel >= 6.2, < 6.6.101'
- 'linux_kernel >= 6.7, < 6.12.40'
- 'linux_kernel >= 6.13, < 6.15.8'
- linux_kernel = 6.16
- debian_linux = 11.0
patched:
- linux_kernel 6.15.8
published: '2025-07-28'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T22:18:42.913'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-38491'
references:
- url: 'https://git.kernel.org/stable/c/1d82a8fe6ee4afdc92f4e8808c9dad2a6095bbc5'
label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- url: 'https://git.kernel.org/stable/c/54999dea879fecb761225e28f274b40662918c30'
label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- url: 'https://git.kernel.org/stable/c/5586518bec27666c747cd52aabb62d485686d0bf'
label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- url: 'https://git.kernel.org/stable/c/75a4c9ab8a7af0d76b31ccd1188ed178c38b35d2'
label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- url: 'https://git.kernel.org/stable/c/f8a1d9b18c5efc76784f5a326e905f641f839894'
label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- url: 'https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html'
label: af854a3a-2127-422b-91ae-364da2661108
- url: 'https://cert-portal.siemens.com/productcert/html/ssa-032379.html'
label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
- nvd
- cve.org
epss: 0.00223
epssPercentile: 0.12778
ssvc:
exploitation: none
automatable: 'yes'
technicalImpact: partial
timestamp: '2026-10-15T21:50:54.238496Z'
ingestedAt: '2026-10-15T22:48:25.509Z'
---
## Overview
In the Linux kernel, the following vulnerability has been resolved:
mptcp: make fallback action and fallback decision atomic
Syzkaller reported the following splat:
WARNING: CPU: 1 PID: 7704 at net/mptcp/protocol.h:1223 __mptcp_do_fallback net/mptcp/protocol.h:1223 [inline]
WARNING: CPU: 1 PID: 7704 at net/mptcp/protocol.h:1223 mptcp_do_fallback net/mptcp/protocol.h:1244 [inline]
WARNING: CPU: 1 PID: 7704 at net/mptcp/protocol.h:1223 check_fully_established net/mptcp/options.c:982 [inline]
WARNING: CPU: 1 PID: 7704 at net/mptcp/protocol.h:1223 mptcp_incoming_options+0x21a8/0x2510 net/mptcp/options.c:1153
Modules linked in:
CPU: 1 UID: 0 PID: 7704 Comm: syz.3.1419 Not tainted 6.16.0-rc3-gbd5ce2324dba #20 PREEMPT(voluntary)
Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__mptcp_do_fallback net/mptcp/protocol.h:1223 [inline]
RIP: 0010:mptcp_do_fallback net/mptcp/protocol.h:1244 [inline]
RIP: 0010:check_fully_established net/mptcp/options.c:982 [inline]
RIP: 0010:mptcp_incoming_options+0x21a8/0x2510 net/mptcp/options.c:1153
Code: 24 18 e8 bb 2a 00 fd e9 1b df ff ff e8 b1 21 0f 00 e8 ec 5f c4 fc 44 0f b7 ac 24 b0 00 00 00 e9 54 f1 ff ff e8 d9 5f c4 fc 90 <0f> 0b 90 e9 b8 f4 ff ff e8 8b 2a 00 fd e9 8d e6 ff ff e8 81 2a 00
RSP: 0018:ffff8880a3f08448 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8880180a8000 RCX: ffffffff84afcf45
RDX: ffff888090223700 RSI: ffffffff84afdaa7 RDI: 0000000000000001
RBP: ffff888017955780 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff8880180a8910 R14: ffff8880a3e9d058 R15: 0000000000000000
FS: 00005555791b8500(0000) GS:ffff88811c495000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2800b7 CR3: 0000000058e44000 CR4: 0000000000350ef0
Call Trace:
tcp_reset+0x26f/0x2b0 net/ipv4/tcp_input.c:4432
tcp_validate_incoming+0x1057/0x1b60 net/ipv4/tcp_input.c:5975
tcp_rcv_established+0x5b5/0x21f0 net/ipv4/tcp_input.c:6166
tcp_v4_do_rcv+0x5dc/0xa70 net/ipv4/tcp_ipv4.c:1925
tcp_v4_rcv+0x3473/0x44a0 net/ipv4/tcp_ipv4.c:2363
ip_protocol_deliver_rcu+0xba/0x480 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x2f1/0x500 net/ipv4/ip_input.c:233
NF_HOOK include/linux/netfilter.h:317 [inline]
NF_HOOK include/linux/netfilter.h:311 [inline]
ip_local_deliver+0x1be/0x560 net/ipv4/ip_input.c:254
dst_input include/net/dst.h:469 [inline]
ip_rcv_finish net/ipv4/ip_input.c:447 [inline]
NF_HOOK include/linux/netfilter.h:317 [inline]
NF_HOOK include/linux/netfilter.h:311 [inline]
ip_rcv+0x514/0x810 net/ipv4/ip_input.c:567
__netif_receive_skb_one_core+0x197/0x1e0 net/core/dev.c:5975
__netif_receive_skb+0x1f/0x120 net/core/dev.c:6088
process_backlog+0x301/0x1360 net/core/dev.c:6440
__napi_poll.constprop.0+0xba/0x550 net/core/dev.c:7453
napi_poll net/core/dev.c:7517 [inline]
net_rx_action+0xb44/0x1010 net/core/dev.c:7644
handle_softirqs+0x1d0/0x770 kernel/softirq.c:579
do_softirq+0x3f/0x90 kernel/softirq.c:480
__local_bh_enable_ip+0xed/0x110 kernel/softirq.c:407
local_bh_enable include/linux/bottom_half.h:33 [inline]
inet_csk_listen_stop+0x2c5/0x1070 net/ipv4/inet_connection_sock.c:1524
mptcp_check_listen_stop.part.0+0x1cc/0x220 net/mptcp/protocol.c:2985
mptcp_check_listen_stop net/mptcp/mib.h:118 [inline]
__mptcp_close+0x9b9/0xbd0 net/mptcp/protocol.c:3000
mptcp_close+0x2f/0x140 net/mptcp/protocol.c:3066
inet_release+0xed/0x200 net/ipv4/af_inet.c:435
inet6_release+0x4f/0x70 net/ipv6/af_inet6.c:487
__sock_release+0xb3/0x270 net/socket.c:649
sock_close+0x1c/0x30 net/socket.c:1439
__fput+0x402/0xb70 fs/file_table.c:465
task_work_run+0x150/0x240 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xd4
---truncated---
## Affected
- `linux_kernel >= 5.10.228, < 5.11`
- `linux_kernel >= 5.15.169, < 5.16`
- `linux_kernel >= 5.19, < 6.1.149`
- `linux_kernel >= 6.2, < 6.6.101`
- `linux_kernel >= 6.7, < 6.12.40`
- `linux_kernel >= 6.13, < 6.15.8`
- `linux_kernel = 6.16`
- `debian_linux = 11.0`
## Remediation
Upgrade past the affected range:
- `linux_kernel 6.15.8`