{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-71126", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-01-13T15:30:19.655Z", "datePublished": "2026-01-14T15:06:11.417Z", "dateUpdated": "2026-08-05T12:12:12.359Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:12:12.359Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: avoid deadlock on fallback while reinjecting\n\nJakub reported an MPTCP deadlock at fallback time:\n\n WARNING: possible recursive locking detected\n 6.18.0-rc7-virtme #1 Not tainted\n --------------------------------------------\n mptcp_connect/20858 is trying to acquire lock:\n ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_try_fallback+0xd8/0x280\n\n but task is already holding lock:\n ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0\n\n other info that might help us debug this:\n Possible unsafe locking scenario:\n\n CPU0\n ----\n lock(&msk->fallback_lock);\n lock(&msk->fallback_lock);\n\n *** DEADLOCK ***\n\n May be due to missing lock nesting notation\n\n 3 locks held by mptcp_connect/20858:\n #0: ff1100001da18290 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_sendmsg+0x114/0x1bc0\n #1: ff1100001db40fd0 (k-sk_lock-AF_INET#2){+.+.}-{0:0}, at: __mptcp_retrans+0x2cb/0xaa0\n #2: ff1100001da18b60 (&msk->fallback_lock){+.-.}-{3:3}, at: __mptcp_retrans+0x352/0xaa0\n\n stack backtrace:\n CPU: 0 UID: 0 PID: 20858 Comm: mptcp_connect Not tainted 6.18.0-rc7-virtme #1 PREEMPT(full)\n Hardware name: Bochs, BIOS Bochs 01/01/2011\n Call Trace:\n \n dump_stack_lvl+0x6f/0xa0\n print_deadlock_bug.cold+0xc0/0xcd\n validate_chain+0x2ff/0x5f0\n __lock_acquire+0x34c/0x740\n lock_acquire.part.0+0xbc/0x260\n _raw_spin_lock_bh+0x38/0x50\n __mptcp_try_fallback+0xd8/0x280\n mptcp_sendmsg_frag+0x16c2/0x3050\n __mptcp_retrans+0x421/0xaa0\n mptcp_release_cb+0x5aa/0xa70\n release_sock+0xab/0x1d0\n mptcp_sendmsg+0xd5b/0x1bc0\n sock_write_iter+0x281/0x4d0\n new_sync_write+0x3c5/0x6f0\n vfs_write+0x65e/0xbb0\n ksys_write+0x17e/0x200\n do_syscall_64+0xbb/0xfd0\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n RIP: 0033:0x7fa5627cbc5e\n 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 c3 83 e2 39 83 fa 08 75 e7 e8 13 ff ff ff 0f 1f 00 f3 0f 1e fa\n RSP: 002b:00007fff1fe14700 EFLAGS: 00000202 ORIG_RAX: 0000000000000001\n RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fa5627cbc5e\n RDX: 0000000000001f9c RSI: 00007fff1fe16984 RDI: 0000000000000005\n RBP: 00007fff1fe14710 R08: 0000000000000000 R09: 0000000000000000\n R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff1fe16920\n R13: 0000000000002000 R14: 0000000000001f9c R15: 0000000000001f9c\n\nThe packet scheduler could attempt a reinjection after receiving an\nMP_FAIL and before the infinite map has been transmitted, causing a\ndeadlock since MPTCP needs to do the reinjection atomically from WRT\nfallback.\n\nAddress the issue explicitly avoiding the reinjection in the critical\nscenario. Note that this is the only fallback critical section that\ncould potentially send packets and hit the double-lock." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:N - MP_FAIL is a peer-supplied TCP option processed through the MPTCP receive path before any application authentication gate ([RFC 8684 ยง3.7](https://www.rfc-editor.org/rfc/rfc8684.html#section-3.7)). An Internet-facing MPTCP service is therefore remotely reachable.\nAC:L - A peer can TCP-ACK outstanding bytes while omitting the DSS Data ACK and carrying MP_FAIL, leaving an MPTCP fragment pending after the TCP queue becomes empty; the normal retransmission timer then reaches the nested-lock path. The peer controls the ACK, MP_FAIL, and timing, so no uncontrollable race is required.\nPR:N - No capability, local account, or application credential is required; any remote endpoint completing the MPTCP handshake can send MP_FAIL, and its handler performs no privilege or credential check.\nUI:N - No human action is required because network packet processing and the retransmission timer drive the deadlock, with ordinary service output supplying the pending fragment.\nS:U - The vulnerable receive and retransmission paths and the resulting lockup are within the same kernel security authority, without crossing a VM, IOMMU, or sandbox boundary.\nC:N - This is a recursive spinlock acquisition with no out-of-bounds access, use-after-free, or information-disclosure primitive.\nI:N - The path deadlocks while updating fallback and retransmission state but does not corrupt memory or provide a write or control-flow primitive.\nA:H - The retransmission path holds fallback_lock and then re-enters __mptcp_try_fallback() through mptcp_sendmsg_frag(), spinning indefinitely on the same lock ([fix commit](https://git.kernel.org/stable/c/ffb8c27b0539dd90262d1021488e 7817fae57c42)). This can lock a CPU or panic the kernel via watchdog and can be repeated across connections." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/mptcp/protocol.c" ], "versions": [ { "version": "5586518bec27666c747cd52aabb62d485686d0bf", "lessThan": "0107442e82c0f8d6010e07e6030741c59c520d6e", "status": "affected", "versionType": "git" }, { "version": "75a4c9ab8a7af0d76b31ccd1188ed178c38b35d2", "lessThan": "252892d5a6a2f163ce18f32716e46fa4da7d4e79", "status": "affected", "versionType": "git" }, { "version": "54999dea879fecb761225e28f274b40662918c30", "lessThan": "0ca9fb4335e726dab4f23b3bfe87271d8f005f41", "status": "affected", "versionType": "git" }, { "version": "f8a1d9b18c5efc76784f5a326e905f641f839894", "lessThan": "50f47c02be419bf0a3ae94c118addf67beef359f", "status": "affected", "versionType": "git" }, { "version": "f8a1d9b18c5efc76784f5a326e905f641f839894", "lessThan": "ffb8c27b0539dd90262d1021488e7817fae57c42", "status": "affected", "versionType": "git" }, { "version": "1d82a8fe6ee4afdc92f4e8808c9dad2a6095bbc5", "status": "affected", "versionType": "git" }, { "version": "6.1.149", "lessThan": "6.1.160", "status": "affected", "versionType": "semver" }, { "version": "6.6.101", "lessThan": "6.6.120", "status": "affected", "versionType": "semver" }, { "version": "6.12.40", "lessThan": "6.12.64", "status": "affected", "versionType": "semver" }, { "version": "6.15.8", "lessThan": "6.16", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/mptcp/protocol.c" ], "versions": [ { "version": "6.16", "status": "affected" }, { "version": "0", "lessThan": "6.16", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.160", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.120", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.64", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.3", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.19", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1.149", "versionEndExcluding": "6.1.160" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6.101", "versionEndExcluding": "6.6.120" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.12.40", "versionEndExcluding": "6.12.64" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.16", "versionEndExcluding": "6.18.3" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.16", "versionEndExcluding": "6.19" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15.8" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/0107442e82c0f8d6010e07e6030741c59c520d6e" }, { "url": "https://git.kernel.org/stable/c/252892d5a6a2f163ce18f32716e46fa4da7d4e79" }, { "url": "https://git.kernel.org/stable/c/0ca9fb4335e726dab4f23b3bfe87271d8f005f41" }, { "url": "https://git.kernel.org/stable/c/50f47c02be419bf0a3ae94c118addf67beef359f" }, { "url": "https://git.kernel.org/stable/c/ffb8c27b0539dd90262d1021488e7817fae57c42" } ], "title": "mptcp: avoid deadlock on fallback while reinjecting", "x_generator": { "engine": "bippy-1.2.0" } } } }