Linux Kernel up to 6.12.108/6.18.49/7.2.3 MPTCP subflow_ulp_clone local_id uninitialized variable

CVSS Meta Temp Score
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CTI Interest Score
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9.5$0-$5k0.00+

Summaryinfo

A vulnerability categorized as very critical has been discovered in Linux Kernel up to 6.12.108/6.18.49/7.2.3. This impacts the function subflow_ulp_clone of the component MPTCP. Executing a manipulation of the argument local_id can lead to uninitialized variable. This vulnerability appears as CVE-2026-89554. The attack may be performed from remote. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.12.108/6.18.49/7.2.3. It has been declared as very critical. This vulnerability affects the function subflow_ulp_clone of the component MPTCP. The manipulation of the argument local_id with an unknown input leads to a uninitialized variable vulnerability. The CWE definition for the vulnerability is CWE-457. The code uses a variable that has not been initialized, leading to unpredictable or unintended results. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-89554 since 09/11/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/12/2026).

Upgrading to version 6.12.109, 6.18.50, 7.2.4 or 7.3-rc1 eliminates this vulnerability. Applying the patch 64f2c5dd49b956a542c8c02b8dad5d262a462bba/51887ccd88791ddaa8755a7c614fda031ecf7982/bf19d166337c6488b39cb03eeeffb30a941d6326/b878dfdd12d7a5b8722a78d35e313506140ca3d9 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

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Version

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 10.0
VulDB Meta Temp Score: 9.5

VulDB Base Score: 10.0
VulDB Temp Score: 9.5
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Uninitialized variable
CWE: CWE-457 / CWE-453
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.12.109/6.18.50/7.2.4/7.3-rc1
Patch: 64f2c5dd49b956a542c8c02b8dad5d262a462bba/51887ccd88791ddaa8755a7c614fda031ecf7982/bf19d166337c6488b39cb03eeeffb30a941d6326/b878dfdd12d7a5b8722a78d35e313506140ca3d9

Timelineinfo

09/11/2026 CVE reserved
09/11/2026 +0 days VulDB entry created
09/12/2026 +0 days Advisory disclosed
09/12/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-89554 (🔒)
GCVE (CVE): GCVE-0-2026-89554
GCVE (VulDB): GCVE-100-402928

Entryinfo

Created: 09/12/2026 01:53
Changes: 09/12/2026 01:53 (60)
Complete: 🔍
Cache ID: 216::103

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