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CVE-2026-89554

HIGHCVSS 8.2/10EPSS 0.56%

Last modified

CVE-2026-89554 is a high-severity vulnerability rated 8.2/10 on the CVSS scale. 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. EPSS estimates a 0.56% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
8.2/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

EPSS Probability
0.56%

44.8th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
LinuxLinux>= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < 4534e0eead692bb069ad1e6a5a245fc2e2078300; >= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < 63cacb05e51a1c6e1349d2e593d00fd6ef43def4; >= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < 954b5ea836eb118d188975ced803448537ab8479; >= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < 9df36a4846375a9b75bf42d77bfed216b0f366f9; >= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < 64f2c5dd49b956a542c8c02b8dad5d262a462bba; >= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < 51887ccd88791ddaa8755a7c614fda031ecf7982; >= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < bf19d166337c6488b39cb03eeeffb30a941d6326; >= 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, < b878dfdd12d7a5b8722a78d35e313506140ca3d9
LinuxLinux5.9

References

Timeline

Published
Last Modified
Status
Received

Frequently Asked Questions

What is 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.
How severe is CVE-2026-89554?
CVE-2026-89554 has a CVSS score of 8.2/10 (HIGH severity). The EPSS model estimates a 0.56% probability of exploitation in the next 30 days.
How do I fix CVE-2026-89554?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST