Linux Kernel up to 6.19-rc1 mptcp mptcp_connect deadlock

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5.0$0-$5k0.00

Summaryinfo

A vulnerability categorized as critical has been discovered in Linux Kernel up to 6.1.159/6.6.119/6.12.63/6.18.2/6.19-rc1. Affected is the function mptcp_connect of the component mptcp. The manipulation results in deadlock. This vulnerability is identified as CVE-2025-71126. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 6.1.159/6.6.119/6.12.63/6.18.2/6.19-rc1. Affected is the function mptcp_connect of the component mptcp. The manipulation with an unknown input leads to a deadlock vulnerability. CWE is classifying the issue as CWE-833. The product contains multiple threads or executable segments that are waiting for each other to release a necessary lock, resulting in deadlock. This is going to have an impact on availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: mptcp: avoid deadlock on fallback while reinjecting Jakub reported an MPTCP deadlock at fallback time: WARNING: possible recursive locking detected 6.18.0-rc7-virtme #1 Not tainted -------------------------------------------- mptcp_connect/20858 is trying to acquire lock: ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_try_fallback+0xd8/0x280 but task is already holding lock: ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&msk->fallback_lock); lock(&msk->fallback_lock); *** DEADLOCK *** May be due to missing lock nesting notation 3 locks held by mptcp_connect/20858: #0: ff1100001da18290 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_sendmsg+0x114/0x1bc0 #1: ff1100001db40fd0 (k-sk_lock-AF_INET#2){+.+.}-{0:0}, at: __mptcp_retrans+0x2cb/0xaa0 #2: ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0 stack backtrace: CPU: 0 UID: 0 PID: 20858 Comm: mptcp_connect Not tainted 6.18.0-rc7-virtme #1 PREEMPT(full) Hardware name: Bochs, BIOS Bochs 01/01/2011 Call Trace: <TASK> dump_stack_lvl+0x6f/0xa0 print_deadlock_bug.cold+0xc0/0xcd validate_chain+0x2ff/0x5f0 __lock_acquire+0x34c/0x740 lock_acquire.part.0+0xbc/0x260 _raw_spin_lock_bh+0x38/0x50 __mptcp_try_fallback+0xd8/0x280 mptcp_sendmsg_frag+0x16c2/0x3050 __mptcp_retrans+0x421/0xaa0 mptcp_release_cb+0x5aa/0xa70 release_sock+0xab/0x1d0 mptcp_sendmsg+0xd5b/0x1bc0 sock_write_iter+0x281/0x4d0 new_sync_write+0x3c5/0x6f0 vfs_write+0x65e/0xbb0 ksys_write+0x17e/0x200 do_syscall_64+0xbb/0xfd0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7fa5627cbc5e Code: 4d 89 d8 e8 14 bd 00 00 4c 8b 5d f8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 11 c9 c3 0f 1f 80 00 00 00 00 48 8b 45 10 0f 05 <c9> c3 83 e2 39 83 fa 08 75 e7 e8 13 ff ff ff 0f 1f 00 f3 0f 1e fa RSP: 002b:00007fff1fe14700 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fa5627cbc5e RDX: 0000000000001f9c RSI: 00007fff1fe16984 RDI: 0000000000000005 RBP: 00007fff1fe14710 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff1fe16920 R13: 0000000000002000 R14: 0000000000001f9c R15: 0000000000001f9c The packet scheduler could attempt a reinjection after receiving an MP_FAIL and before the infinite map has been transmitted, causing a deadlock since MPTCP needs to do the reinjection atomically from WRT fallback. Address the issue explicitly avoiding the reinjection in the critical scenario. Note that this is the only fallback critical section that could potentially send packets and hit the double-lock.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2025-71126 since 01/13/2026. The exploitability is told to be difficult. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 284793 (Linux Distros Unpatched Vulnerability : CVE-2025-71126), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.1.160, 6.6.120, 6.12.64, 6.18.3 or 6.19-rc2 eliminates this vulnerability. Applying the patch 0107442e82c0f8d6010e07e6030741c59c520d6e/252892d5a6a2f163ce18f32716e46fa4da7d4e79/0ca9fb4335e726dab4f23b3bfe87271d8f005f41/50f47c02be419bf0a3ae94c118addf67beef359f/ffb8c27b0539dd90262d1021488e7817fae57c42 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (284793) and CERT Bund (WID-SEC-2026-0119). Once again VulDB remains the best source for vulnerability data.

Affected

  • Open Source Linux Kernel

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.1
VulDB Meta Temp Score: 5.0

VulDB Base Score: 4.8
VulDB Temp Score: 4.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.5
NVD Vector: 🔒

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Deadlock
CWE: CWE-833 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 284793
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-71126

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.1.160/6.6.120/6.12.64/6.18.3/6.19-rc2
Patch: 0107442e82c0f8d6010e07e6030741c59c520d6e/252892d5a6a2f163ce18f32716e46fa4da7d4e79/0ca9fb4335e726dab4f23b3bfe87271d8f005f41/50f47c02be419bf0a3ae94c118addf67beef359f/ffb8c27b0539dd90262d1021488e7817fae57c42

Timelineinfo

01/13/2026 CVE reserved
01/14/2026 +1 days Advisory disclosed
01/14/2026 +0 days VulDB entry created
03/25/2026 +70 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-71126 (🔒)
GCVE (CVE): GCVE-0-2025-71126
GCVE (VulDB): GCVE-100-341076
CERT Bund: WID-SEC-2026-0119 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 01/14/2026 17:28
Updated: 03/25/2026 22:03
Changes: 01/14/2026 17:28 (59), 01/16/2026 02:21 (2), 01/16/2026 05:59 (7), 03/25/2026 22:03 (12)
Complete: 🔍
Cache ID: 216::103

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