Answer in brief
CVE-2026-89554 records a Unknown severity vulnerability in mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <64f2c5dd49b956a542c8c02b8dad5d262a462bba || >=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <51887ccd88791ddaa8755a7c614fda031ecf7982 || >=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <bf19d166337c6488b39cb03eeeffb30a941d6326 || >=9466a1ccebbe54ac57fb8a89c2b4b854826546a8 <b878dfdd12d7a5b8722a78d35e313506140ca3d9 | 64f2c5dd49b956a542c8c02b8dad5d262a462bba, 51887ccd88791ddaa8755a7c614fda031ecf7982, bf19d166337c6488b39cb03eeeffb30a941d6326, b878dfdd12d7a5b8722a78d35e313506140ca3d9 |
| Linux/Linuxgeneric | 5.9 | Not reported |
Published upstream
Sep 11, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 11, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 11, 2026
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.
Quoted source text, attributed separately from HOL analysis.