Linux KernelOperating system · Linux
CVE-2025-21705
A fix is available.
Upgrade to 6.1.129 / 6.4 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click
Patch available
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn the Linux kernel, the following vulnerability has been resolved: mptcp: handle fastopen disconnect correctly Syzbot was able to trigger a data stream corruption: WARNING: CPU: 0 PID: 9846 at net/mptcp/protocol.c:1024 __mptcp_clean_una+0xddb/0xff0 net/mptcp/protocol.c:1024 Modules linked in: CPU: 0 UID: 0 PID: 9846 Comm: syz-executor351 Not tainted 6.13.0-rc2-syzkaller-00059-g00a5acdbf398 #0 Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 11/25/2024 RIP: 0010:__mptcp_clean_una+0xddb/0xff0 net/mptcp/protocol.c:1024 Code: fa ff ff 48 8b 4c 24 18 80 e1 07 fe c1 38 c1 0f 8c 8e fa ff ff 48 8b 7c 24 18 e8 e0 db 54 f6 e9 7f fa ff ff e8 e6 80 ee f5 90 <0f> 0b 90 4c 8b 6c 24 40 4d 89 f4 e9 04 f5 ff ff 44 89 f1 80 e1 07 RSP: 0018:ffffc9000c0cf400 EFLAGS: 00010293 RAX: ffffffff8bb0dd5a RBX: ffff888033f5d230 RCX: ffff888059ce8000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffc9000c0cf518 R08: ffffffff8bb0d1dd R09: 1ffff110170c8928 R10: dffffc0000000000 R11: ffffed10170c8929 R12: 0000000000000000 R13: ffff888033f5d220 R14: dffffc0000000000 R15: ffff8880592b8000 FS: 00007f6e866496c0(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f6e86f491a0 CR3: 00000000310e6000 CR4: 00000000003526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> __mptcp_clean_una_wakeup+0x7f/0x2d0 net/mptcp/protocol.c:1074 mptcp_release_cb+0x7cb/0xb30 net/mptcp/protocol.c:3493 release_sock+0x1aa/0x1f0 net/core/sock.c:3640 inet_wait_for_connect net/ipv4/af_inet.c:609 [inline] __inet_stream_connect+0x8bd/0xf30 net/ipv4/af_inet.c:703 mptcp_sendmsg_fastopen+0x2a2/0x530 net/mptcp/protocol.c:1755 mptcp_sendmsg+0x1884/0x1b10 net/mptcp/protocol.c:1830 sock_sendmsg_nosec net/socket.c:711 [inline] __sock_sendmsg+0x1a6/0x270 net/socket.c:726 ____sys_sendmsg+0x52a/0x7e0 net/socket.c:2583 ___sys_sendmsg net/socket.c:2637 [inline] __sys_sendmsg+0x269/0x350 net/socket.c:2669 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f6e86ebfe69 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 1f 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f6e86649168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f6e86f491b8 RCX: 00007f6e86ebfe69 RDX: 0000000030004001 RSI: 0000000020000080 RDI: 0000000000000003 RBP: 00007f6e86f491b0 R08: 00007f6e866496c0 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6e86f491bc R13: 000000000000006e R14: 00007ffe445d9420 R15: 00007ffe445d9508 </TASK> The root cause is the bad handling of disconnect() generated internally by the MPTCP protocol in case of connect FASTOPEN errors. Address the issue increasing the socket disconnect counter even on such a case, to allow other threads waiting on the same socket lock to properly error out.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisA detailed technical summary for this CVE is being prepared.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Linux KernelOperating system
Affected:
>= 6.1.36, < 6.1.129>= 6.3.10, < 6.4>= 6.4.1, < 6.6.76>= 6.7, < 6.12.13>= 6.13, < 6.13.2= 6.4CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped
Upgrade available
Upgrade to 6.1.129 / 6.4 / 6.6.76 or later
Fixed in
6.1.1296.46.6.76
Vendor patch
git.kernel.org →
Recommended fix
High confidence
6.1.129 (for 6.1.x), 6.6.76 (for 6.4.x-6.6.x), or 6.12.13 (for 6.7.x-6.12.x)
- Identify the currently running kernel version using `uname -r`
- Determine which version range your current kernel falls into (6.1.x, 6.4.x-6.6.x, or 6.7.x-6.12.x)
- Upgrade to a fixed kernel version: for 6.1.x line upgrade to >= 6.1.129, for 6.4.x-6.6.x line upgrade to >= 6.6.76, for 6.7.x-6.12.x line upgrade to >= 6.12.13
- After kernel upgrade, reboot the system to load the fixed kernel
- Verify the fix is applied by checking the kernel version matches or exceeds the appropriate fixed release
Caveat Kernel upgrades may require system reboot and could introduce compatibility issues with custom modules or specific hardware drivers; ensure dependent kernel modules are compatible with the new kernel version
Generated from the published advisory — verify against the referenced sources before acting.
We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600.
Get the upgrade done
Scan for this in your stack
Free · runs locally
dbcve dependency scanner
Check whether your project pulls in CVE-2025-21705 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-21705 in production — separate from our analysis above.
Know something about CVE-2025-21705?
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
What this is
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
What belongs here
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data