CVE-2026-97568
Received Received - Intake

MPTCP Syncookie Request Backup Flag Handling Issue

Publication date: 2026-09-25

Last updated on: 2026-09-25

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: mptcp: syncookies: remember the request backup flag Instead of using an uninitialised bit when copying the info in subflow_ulp_clone(). To fix this, no need to extend the join_entry structure: backup is coming from struct mptcp_subflow_request_sock, only one bit. Do the same here by using one bit for both.

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Meta Information

Published
2026-09-25
Last Modified
2026-09-25
Generated
2026-09-25
AI Q&A
2026-09-25
EPSS Evaluated
N/A
NVD
CVE-2026-97568
EUVD
EUVD-2026-86876

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves improper handling of the request backup flag in the MPTCP (Multipath TCP) syncookies implementation. The issue arises when copying information in the subflow_ulp_clone() function, where an uninitialized bit is used instead of properly tracking the backup flag. The fix ensures the backup flag is correctly managed by using a single bit from the existing mptcp_subflow_request_sock structure.

Detection Guidance

This vulnerability is specific to the Linux kernel's MPTCP (Multipath TCP) implementation. Detection requires checking kernel logs for MPTCP-related errors or crashes. Use commands like 'dmesg | grep mptcp' or 'journalctl -k | grep mptcp' to search for relevant messages. If syncookie-related issues are suspected, monitor for connection failures or unexpected behavior in MPTCP sessions.

Impact Analysis

This vulnerability could potentially allow an attacker to manipulate MPTCP connections by exploiting the improper handling of the backup flag. This might lead to unexpected behavior in network connections, such as connection drops or unauthorized data transmission. However, the impact is likely limited to systems using MPTCP with syncookies enabled.

Mitigation Strategies

Apply the latest kernel update from your Linux distribution to patch this vulnerability. If immediate patching is not possible, consider disabling MPTCP temporarily by setting 'net.mptcp.enabled=0' via sysctl or removing MPTCP support from the kernel. Monitor vendor advisories for updates and test changes in a non-production environment first.

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