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UBUNTU-CVE-2025-68291 Not scored

UBUNTU-CVE-2025-68291

In the Linux kernel, the following vulnerability has been resolved: mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose(). syzbot reported divide-by-zero in __tcp_select_window() by MPTCP socket. [0] We had a similar issue for the bare TCP and fixed in commit 499350a5a6e7 ("tcp: initialize rcv_mss to TCP_MIN_MSS instead of 0"). Let's apply the same fix to mptcp_do_fastclose(). [0]: Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 0 UID: 0 PID: 6068 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:__tcp_select_window+0x824/0x1320 net/ipv4/tcp_output.c:3336 Code: ff ff ff 44 89 f1 d3 e0 89 c1 f7 d1 41 01 cc 41 21 c4 e9 a9 00 00 00 e8 ca 49 01 f8 e9 9c 00 00 00 e8 c0 49 01 f8 44 89 e0 99 <f7> 7c 24 1c 41 29 d4 48 bb 00 00 00 00 00 fc ff df e9 80 00 00 00 RSP: 0018:ffffc90003017640 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88807b469e40 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffc90003017730 R08: ffff888033268143 R09: 1ffff1100664d028 R10: dffffc0000000000 R11: ffffed100664d029 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 000055557faa0500(0000) GS:ffff888126135000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f64a1912ff8 CR3: 0000000072122000 CR4: 00000000003526f0 Call Trace: <TASK> tcp_select_window net/ipv4/tcp_output.c:281 [inline] __tcp_transmit_skb+0xbc7/0x3aa0 net/ipv4/tcp_output.c:1568 tcp_transmit_skb net/ipv4/tcp_output.c:1649 [inline] tcp_send_active_reset+0x2d1/0x5b0 net/ipv4/tcp_output.c:3836 mptcp_do_fastclose+0x27e/0x380 net/mptcp/protocol.c:2793 mptcp_disconnect+0x238/0x710 net/mptcp/protocol.c:3253 mptcp_sendmsg_fastopen+0x2f8/0x580 net/mptcp/protocol.c:1776 mptcp_sendmsg+0x1774/0x1980 net/mptcp/protocol.c:1855 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0xe5/0x270 net/socket.c:742 __sys_sendto+0x3bd/0x520 net/socket.c:2244 __do_sys_sendto net/socket.c:2251 [inline] __se_sys_sendto net/socket.c:2247 [inline] __x64_sys_sendto+0xde/0x100 net/socket.c:2247 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f66e998f749 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffff9acedb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00007f66e9be5fa0 RCX: 00007f66e998f749 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003 RBP: 00007ffff9acee10 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 00007f66e9be5fa0 R14: 00007f66e9be5fa0 R15: 0000000000000006 </TASK>

Exploit probability Not scored
Published December 16, 2025
Required by Not available
Last source change August 17, 2026

02 / AFFECTED SOFTWARE

Affected packages

Ubuntu:22.04:LTS linux-starfive-6.5

11 explicit affected versions

Ubuntu:18.04:LTS linux-oem

50 explicit affected versions

Ubuntu:18.04:LTS linux-aws-5.0

6 explicit affected versions

Ubuntu:20.04:LTS linux-aws-5.11

12 explicit affected versions

Ubuntu:22.04:LTS linux-oem-6.5

19 explicit affected versions

Ubuntu:20.04:LTS linux-raspi2

6 explicit affected versions

Ubuntu:24.04:LTS linux-riscv

24 explicit affected versions

Ubuntu:22.04:LTS linux-riscv-6.5

10 explicit affected versions

Ubuntu:22.04:LTS linux-ibm-6.8

32 explicit affected versions

Ubuntu:24.04:LTS linux-oem-6.8

26 explicit affected versions

Ubuntu:22.04:LTS linux-azure-5.19

7 explicit affected versions

Ubuntu:22.04:LTS linux-oracle-6.8

35 explicit affected versions

Ubuntu:22.04:LTS linux-gcp-6.5

13 explicit affected versions

Ubuntu:24.04:LTS linux-nvidia

39 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.14

35 explicit affected versions

Ubuntu:20.04:LTS linux-gke-5.15

18 explicit affected versions

Ubuntu:24.04:LTS linux-oracle

40 explicit affected versions

Ubuntu:20.04:LTS linux-aws-5.13

13 explicit affected versions

Ubuntu:20.04:LTS linux-aws-5.8

4 explicit affected versions

Ubuntu:16.04:LTS linux-hwe-edge

23 explicit affected versions

Ubuntu:24.04:LTS linux

47 explicit affected versions

Ubuntu:24.04:LTS linux-raspi-realtime

1 explicit affected versions

Ubuntu:20.04:LTS linux-hwe-5.8

21 explicit affected versions

Ubuntu:20.04:LTS linux-hwe-5.13

16 explicit affected versions

Ubuntu:22.04:LTS linux-lowlatency-hwe-6.2

10 explicit affected versions

Ubuntu:24.04:LTS linux-aws

43 explicit affected versions

Ubuntu:24.04:LTS linux-hwe-6.11

8 explicit affected versions

Ubuntu:18.04:LTS linux-oracle-5.0

7 explicit affected versions

Ubuntu:20.04:LTS linux-riscv

12 explicit affected versions

Ubuntu:24.04:LTS linux-azure-6.11

7 explicit affected versions

Ubuntu:20.04:LTS linux-gcp-5.11

12 explicit affected versions

Ubuntu:22.04:LTS linux-azure-6.5

14 explicit affected versions

Ubuntu:22.04:LTS linux-intel-iot-realtime

1 explicit affected versions

Ubuntu:20.04:LTS linux-intel-5.13

7 explicit affected versions

Ubuntu:24.04:LTS linux-nvidia-tegra

11 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.13

12 explicit affected versions

Ubuntu:20.04:LTS linux-oracle-5.11

12 explicit affected versions

Ubuntu:Pro:Realtime:22.04:LTS linux-realtime-6.8

36 explicit affected versions

Ubuntu:22.04:LTS linux-azure-6.8

25 explicit affected versions

Ubuntu:24.04:LTS linux-gkeop

29 explicit affected versions

Ubuntu:18.04:LTS linux-hwe-edge

10 explicit affected versions

Ubuntu:18.04:LTS linux-gke-5.4

37 explicit affected versions

Ubuntu:22.04:LTS linux-oracle-6.5

13 explicit affected versions

Ubuntu:22.04:LTS linux-lowlatency-hwe-6.8

35 explicit affected versions

Ubuntu:22.04:LTS linux-azure-fde-6.2

10 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.10

26 explicit affected versions

Ubuntu:Pro:FIPS-updates:24.04:LTS linux-azure-fips

6 explicit affected versions

Ubuntu:20.04:LTS linux-gcp-5.13

13 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.6

29 explicit affected versions

Ubuntu:18.04:LTS linux-gcp-5.3

13 explicit affected versions

Ubuntu:24.04:LTS linux-riscv-6.14

12 explicit affected versions

Ubuntu:24.04:LTS linux-nvidia-lowlatency

36 explicit affected versions

Ubuntu:22.04:LTS linux-gcp-6.8

36 explicit affected versions

Ubuntu:18.04:LTS linux-gke-4.15

33 explicit affected versions

Ubuntu:22.04:LTS linux-riscv

23 explicit affected versions

Ubuntu:18.04:LTS linux-aws-5.3

10 explicit affected versions

Ubuntu:Pro:FIPS-updates:24.04:LTS linux-fips

15 explicit affected versions

Ubuntu:Pro:FIPS-updates:24.04:LTS linux-gcp-fips

14 explicit affected versions

Ubuntu:Nvidia-BlueField:24.04:LTS linux-bluefield

11 explicit affected versions

Ubuntu:20.04:LTS linux-hwe-5.11

12 explicit affected versions

Ubuntu:20.04:LTS linux-azure-5.8

7 explicit affected versions

Ubuntu:22.04:LTS linux-gcp-6.2

12 explicit affected versions

Ubuntu:22.04:LTS linux-lowlatency-hwe-5.19

10 explicit affected versions

Ubuntu:22.04:LTS linux-oem-5.17

26 explicit affected versions

Ubuntu:24.04:LTS linux-azure

34 explicit affected versions

Ubuntu:22.04:LTS linux-hwe-6.8

30 explicit affected versions

Ubuntu:24.04:LTS linux-raspi

42 explicit affected versions

Ubuntu:22.04:LTS linux-azure-6.2

13 explicit affected versions

Ubuntu:24.04:LTS linux-ibm

41 explicit affected versions

Ubuntu:22.04:LTS linux-oem-6.0

16 explicit affected versions

Ubuntu:24.04:LTS linux-gcp

45 explicit affected versions

Ubuntu:22.04:LTS linux-azure-fde-5.19

3 explicit affected versions

Ubuntu:24.04:LTS linux-gcp-6.11

7 explicit affected versions

Ubuntu:20.04:LTS linux-gke

51 explicit affected versions

Ubuntu:24.04:LTS linux-oem-6.11

18 explicit affected versions

Ubuntu:Pro:Realtime:24.04:LTS linux-raspi-realtime

37 explicit affected versions

Ubuntu:20.04:LTS linux-azure-5.13

12 explicit affected versions

Ubuntu:22.04:LTS linux-oem-6.1

27 explicit affected versions

Ubuntu:22.04:LTS linux-nvidia-6.8

38 explicit affected versions

Ubuntu:22.04:LTS linux-gcp-5.19

8 explicit affected versions

Ubuntu:20.04:LTS linux-oracle-5.8

5 explicit affected versions

Ubuntu:22.04:LTS linux-riscv-5.19

8 explicit affected versions

Ubuntu:22.04:LTS linux-hwe-6.2

10 explicit affected versions

Ubuntu:24.04:LTS linux-lowlatency-hwe-6.11

7 explicit affected versions

Ubuntu:Pro:Realtime:24.04:LTS linux-realtime

41 explicit affected versions

Ubuntu:22.04:LTS linux-lowlatency-hwe-6.5

13 explicit affected versions

Ubuntu:20.04:LTS linux-azure-5.11

13 explicit affected versions

Ubuntu:22.04:LTS linux-starfive-5.19

7 explicit affected versions

Ubuntu:24.04:LTS linux-nvidia-6.11

8 explicit affected versions

Ubuntu:20.04:LTS linux-riscv-5.8

10 explicit affected versions

Ubuntu:20.04:LTS linux-oracle-5.13

12 explicit affected versions

Ubuntu:18.04:LTS linux-azure

44 explicit affected versions

Ubuntu:18.04:LTS linux-azure-5.3

16 explicit affected versions

Ubuntu:22.04:LTS linux-starfive-6.2

3 explicit affected versions

Ubuntu:20.04:LTS linux-riscv-5.11

13 explicit affected versions

Ubuntu:20.04:LTS linux-azure-fde

26 explicit affected versions

Ubuntu:20.04:LTS linux-gkeop-5.15

45 explicit affected versions

Ubuntu:18.04:LTS linux-gkeop-5.4

37 explicit affected versions

Ubuntu:24.04:LTS linux-lowlatency

46 explicit affected versions

Ubuntu:22.04:LTS linux-aws-6.5

14 explicit affected versions

Ubuntu:18.04:LTS linux-gcp

38 explicit affected versions

Ubuntu:18.04:LTS linux-oracle-5.3

9 explicit affected versions

Ubuntu:22.04:LTS linux-hwe-5.19

11 explicit affected versions

Ubuntu:22.04:LTS linux-riscv-6.8

34 explicit affected versions

Ubuntu:22.04:LTS linux-nvidia-6.2

7 explicit affected versions

Ubuntu:20.04:LTS linux-gcp-5.8

4 explicit affected versions

Ubuntu:24.04:LTS linux-realtime

1 explicit affected versions

Ubuntu:22.04:LTS linux-hwe-6.5

13 explicit affected versions

Ubuntu:18.04:LTS linux-hwe

43 explicit affected versions

Ubuntu:22.04:LTS linux-aws-5.19

10 explicit affected versions

Ubuntu:22.04:LTS linux-allwinner-5.19

8 explicit affected versions

Ubuntu:24.04:LTS linux-gke

40 explicit affected versions

Ubuntu:22.04:LTS linux-aws-6.2

14 explicit affected versions

Ubuntu:18.04:LTS linux-azure-edge

4 explicit affected versions

Ubuntu:20.04:LTS linux-gkeop

78 explicit affected versions

Ubuntu:22.04:LTS linux-nvidia-6.5

11 explicit affected versions

Ubuntu:22.04:LTS linux-realtime

1 explicit affected versions

Ubuntu:Pro:FIPS-updates:24.04:LTS linux-aws-fips

14 explicit affected versions

Ubuntu:22.04:LTS linux-aws-6.8

34 explicit affected versions

03 / CONNECTIONS

Connected vulnerabilities

04 / EVIDENCE

Source records

Open Source Vulnerabilities UBUNTU-CVE-2025-68291

In the Linux kernel, the following vulnerability has been resolved: mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose(). syzbot reported divide-by-zero in __tcp_select_window() by MPTCP socket. [0] We had a similar issue for the bare TCP and fixed in commit 499350a5a6e7 ("tcp: initialize rcv_mss to TCP_MIN_MSS instead of 0"). Let's apply the same fix to mptcp_do_fastclose(). [0]: Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 0 UID: 0 PID: 6068 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:__tcp_select_window+0x824/0x1320 net/ipv4/tcp_output.c:3336 Code: ff ff ff 44 89 f1 d3 e0 89 c1 f7 d1 41 01 cc 41 21 c4 e9 a9 00 00 00 e8 ca 49 01 f8 e9 9c 00 00 00 e8 c0 49 01 f8 44 89 e0 99 <f7> 7c 24 1c 41 29 d4 48 bb 00 00 00 00 00 fc ff df e9 80 00 00 00 RSP: 0018:ffffc90003017640 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88807b469e40 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffc90003017730 R08: ffff888033268143 R09: 1ffff1100664d028 R10: dffffc0000000000 R11: ffffed100664d029 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 000055557faa0500(0000) GS:ffff888126135000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f64a1912ff8 CR3: 0000000072122000 CR4: 00000000003526f0 Call Trace: <TASK> tcp_select_window net/ipv4/tcp_output.c:281 [inline] __tcp_transmit_skb+0xbc7/0x3aa0 net/ipv4/tcp_output.c:1568 tcp_transmit_skb net/ipv4/tcp_output.c:1649 [inline] tcp_send_active_reset+0x2d1/0x5b0 net/ipv4/tcp_output.c:3836 mptcp_do_fastclose+0x27e/0x380 net/mptcp/protocol.c:2793 mptcp_disconnect+0x238/0x710 net/mptcp/protocol.c:3253 mptcp_sendmsg_fastopen+0x2f8/0x580 net/mptcp/protocol.c:1776 mptcp_sendmsg+0x1774/0x1980 net/mptcp/protocol.c:1855 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0xe5/0x270 net/socket.c:742 __sys_sendto+0x3bd/0x520 net/socket.c:2244 __do_sys_sendto net/socket.c:2251 [inline] __se_sys_sendto net/socket.c:2247 [inline] __x64_sys_sendto+0xde/0x100 net/socket.c:2247 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f66e998f749 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffff9acedb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00007f66e9be5fa0 RCX: 00007f66e998f749 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003 RBP: 00007ffff9acee10 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 00007f66e9be5fa0 R14: 00007f66e9be5fa0 R15: 0000000000000006 </TASK>

View original source

05 / REFERENCES

Further evidence