CVE-2026-89554

mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction

State: Published
Severity: 8.2 High
Published: Sep 11, 2026
Updated: Oct 19, 2026
Reserved: Sep 11, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	8.2 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H	Linux

Weaknesses

The record names no weakness.

Affected Products

Product	Versions
LinuxLinux	9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 4534e0eead692bb069ad1e6a5a245fc2e2078300Affected 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 63cacb05e51a1c6e1349d2e593d00fd6ef43def4Affected 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 954b5ea836eb118d188975ced803448537ab8479Affected 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 9df36a4846375a9b75bf42d77bfed216b0f366f9Affected 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 64f2c5dd49b956a542c8c02b8dad5d262a462bbaAffected 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 51887ccd88791ddaa8755a7c614fda031ecf7982Affected 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before bf19d166337c6488b39cb03eeeffb30a941d6326Affected 9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before b878dfdd12d7a5b8722a78d35e313506140ca3d9Affected
LinuxLinux	5.9Affected before 5.9Not affected 5.10.270 through 5.10.Not affected 5.15.221 through 5.15.Not affected 6.1.188 through 6.1.Not affected 6.6.157 through 6.6.Not affected 6.12.109 through 6.12.Not affected 6.18.50 through 6.18.Not affected 7.2.4 through 7.2.*Not affected 7.3 and laterNot affected

Product

Versions

LinuxLinux

9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 4534e0eead692bb069ad1e6a5a245fc2e2078300Affected
9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 63cacb05e51a1c6e1349d2e593d00fd6ef43def4Affected
9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 954b5ea836eb118d188975ced803448537ab8479Affected
9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 9df36a4846375a9b75bf42d77bfed216b0f366f9Affected
9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 64f2c5dd49b956a542c8c02b8dad5d262a462bbaAffected
9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 51887ccd88791ddaa8755a7c614fda031ecf7982Affected
9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before bf19d166337c6488b39cb03eeeffb30a941d6326Affected
9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before b878dfdd12d7a5b8722a78d35e313506140ca3d9Affected

LinuxLinux

5.9Affected
before 5.9Not affected
5.10.270 through 5.10.*Not affected
5.15.221 through 5.15.*Not affected
6.1.188 through 6.1.*Not affected
6.6.157 through 6.6.*Not affected
6.12.109 through 6.12.*Not affected
6.18.50 through 6.18.*Not affected
7.2.4 through 7.2.*Not affected
7.3 and laterNot affected

References

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