GHSA-9VJ3-QJQ5-H6JG
Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-14 15:32In the Linux kernel, the following vulnerability has been resolved:
mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction
mptcp_token_join_cookie_init_state() restores remote_nonce, local_nonce, backup, join_id, token and msk from the saved cookie entry when rebuilding the request socket for a MP_JOIN 4th-ACK handled under SYN cookies, but it does not restore local_id, even though the SYN path saved it. subflow_ulp_clone() then reads that uninitialized field and stores it as the joined subflow's address-ID. Because the request-sock slab is SLAB_TYPESAFE_BY_RCU and not zeroed on allocation, the value is the stale byte of a previously freed request socket, which an off-path peer can influence by sending concurrent MP_JOIN SYNs. This corrupts the path manager's id-based subflow bookkeeping for the connection.
Restore subflow_req->local_id from the cookie entry, as done for the other fields.
{
"affected": [],
"aliases": [
"CVE-2026-89554"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-11T20:19:39Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction\n\nmptcp_token_join_cookie_init_state() restores remote_nonce, local_nonce,\nbackup, join_id, token and msk from the saved cookie entry when rebuilding\nthe request socket for a MP_JOIN 4th-ACK handled under SYN cookies, but it\ndoes not restore local_id, even though the SYN path saved it.\nsubflow_ulp_clone() then reads that uninitialized field and stores it as\nthe joined subflow\u0027s address-ID. Because the request-sock slab is\nSLAB_TYPESAFE_BY_RCU and not zeroed on allocation, the value is the stale\nbyte of a previously freed request socket, which an off-path peer can\ninfluence by sending concurrent MP_JOIN SYNs. This corrupts the path\nmanager\u0027s id-based subflow bookkeeping for the connection.\n\nRestore subflow_req-\u003elocal_id from the cookie entry, as done for the other\nfields.",
"id": "GHSA-9vj3-qjq5-h6jg",
"modified": "2026-09-14T15:32:29Z",
"published": "2026-09-11T21:31:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89554"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4534e0eead692bb069ad1e6a5a245fc2e2078300"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/51887ccd88791ddaa8755a7c614fda031ecf7982"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/63cacb05e51a1c6e1349d2e593d00fd6ef43def4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/64f2c5dd49b956a542c8c02b8dad5d262a462bba"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/954b5ea836eb118d188975ced803448537ab8479"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9df36a4846375a9b75bf42d77bfed216b0f366f9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b878dfdd12d7a5b8722a78d35e313506140ca3d9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/bf19d166337c6488b39cb03eeeffb30a941d6326"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H",
"type": "CVSS_V3"
}
]
}
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