# CVE-2025-68291: linux: In the Linux kernel, the following vulnerability has been resolved:  mptcp: Initialise rcv_mss before calling tcp_sen...

CVE-2025-68291 is fixed in linux on 1 platform, first by DEBIAN-CVE-2025-68291, released December 16, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2025-68291
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Dec 16, 2025

## Description

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>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.162-1 | [DEBIAN-CVE-2025-68291](https://patchblox.com/security/data/fix/linux/debian-cve-2025-68291.md) | Dec 16, 2025 |
| Linux | linux Debian 14 | 6.17.11-1 | [DEBIAN-CVE-2025-68291](https://patchblox.com/security/data/fix/linux/debian-cve-2025-68291.md) | Dec 16, 2025 |

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