{"id":"CVE-2026-89554","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-89554","summary":"mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction","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's 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's id-based subflow bookkeeping for the connection.\n\nRestore subflow_req->local_id from the cookie entry, as done for the other\nfields.","published":"2026-09-11T19:44:27.586Z","modified":"2026-09-14T03:46:15.093684630Z","cvss":{"score":8.2,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.12.109"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/51887ccd88791ddaa8755a7c614fda031ecf7982"},{"type":"WEB","url":"https://git.kernel.org/stable/c/64f2c5dd49b956a542c8c02b8dad5d262a462bba"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b878dfdd12d7a5b8722a78d35e313506140ca3d9"},{"type":"WEB","url":"https://git.kernel.org/stable/c/bf19d166337c6488b39cb03eeeffb30a941d6326"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89554.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89554"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-14T03:46:15.093684630Z"}}