CVE-2026-89554

In 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.

CVSS v3 8.2 HIGH

8.2^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 4.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://git.kernel.org/stable/c/4534e0eead692bb069ad1e6a5a245fc2e2078300
https://git.kernel.org/stable/c/51887ccd88791ddaa8755a7c614fda031ecf7982
https://git.kernel.org/stable/c/63cacb05e51a1c6e1349d2e593d00fd6ef43def4
https://git.kernel.org/stable/c/64f2c5dd49b956a542c8c02b8dad5d262a462bba
https://git.kernel.org/stable/c/954b5ea836eb118d188975ced803448537ab8479
https://git.kernel.org/stable/c/9df36a4846375a9b75bf42d77bfed216b0f366f9
https://git.kernel.org/stable/c/b878dfdd12d7a5b8722a78d35e313506140ca3d9
https://git.kernel.org/stable/c/bf19d166337c6488b39cb03eeeffb30a941d6326

Configurations

No configuration.

History

No history.

Information

Published : 2026-09-11 20:19

Updated : 2026-09-14 13:19

NVD link : CVE-2026-89554

Mitre link : CVE-2026-89554

CVE.ORG link : CVE-2026-89554

JSON object : View

Products Affected

No product.

CWE

No CWE.

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{"url": "https://git.kernel.org/stable/c/9df36a4846375a9b75bf42d77bfed216b0f366f9", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/b878dfdd12d7a5b8722a78d35e313506140ca3d9", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/bf19d166337c6488b39cb03eeeffb30a941d6326", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "vulnStatus": "Received", "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2026-09-14T13:19:10.453", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}