An uninitialized local_id vulnerability in the Linux kernel MPTCP subsystem exposes systems to potential connection state corruption and denial of service.

This vulnerability occurs in the MPTCP subsystem when handling MP_JOIN requests under SYN cookies. Because the kernel fails to properly initialize the local_id field during socket reconstruction, an unauthenticated remote attacker can influence this value to corrupt the path manager's bookkeeping for the connection.

The exploitation of this flaw can lead to a denial of service by disrupting network connections or potentially causing unexpected behavior in MPTCP-enabled services. With a CVSS score of 8.2, this high-severity vulnerability poses a significant risk to the availability and integrity of network traffic, particularly in environments relying on Multipath TCP for robust connectivity.

Immediate Action: Update the Linux kernel to version 6.12.109, 6.18.50, 7.2.4, or a later stable release provided by your distribution vendor.

Proactive Monitoring: Monitor system logs for unusual MPTCP connection errors or signs of network instability that may indicate attempts to trigger subflow bookkeeping corruption.

Compensating Controls: If patching is not immediately feasible, consider disabling MPTCP support at the kernel level if the feature is not strictly required for network operations.

Public Exploit Available: Unknown.

Given the potential for network-level disruption and the high CVSS severity, administrators should prioritize updating kernel packages across all affected infrastructure. Testing the updated kernel versions in a staging environment is recommended to ensure compatibility, followed by a phased deployment to production systems to mitigate the risk of connection state corruption.