CVE-2026-97566 Linux CVE debrief

Who should care

Linux kernel developers and administrators responsible for maintaining and securing Linux-based systems should assess exposure and verify kernel versions. They should review system configurations, monitor system logs, and perform vulnerability management to ensure the MPTCP path manager is properly configured and secured.

Why it matters

A vulnerability in the Linux kernel's MPTCP path manager can lead to WARN_ON_ONCE(mptcp_pm_is_kernel()) errors. Defenders should verify kernel versions, review system configurations, and monitor system logs.

• Verify kernel updates to ensure MPTCP path manager is properly cleaning up ADD_ADDR announcements
• Monitor system logs for WARN_ON_ONCE(mptcp_pm_is_kernel()) errors
• Review system configurations for MPTCP path manager

Technical summary

The Linux kernel's MPTCP path manager can leave a stale ADD_ADDR announcement entry alive when removing the id 0 endpoint. This can lead to a WARN_ON_ONCE(mptcp_pm_is_kernel()) in mptcp_pm_announced_alloc(). The issue is caused by asymmetry between removal paths for non-zero and id 0 endpoints. The non-zero id path calls mptcp_pm_remove_announced() to clean up, while the id 0 path does not. To fix this, the id 0 path should be made symmetric by calling mptcp_pm_announced_remove() and decrementing add_addr_signaled before queuing the RM_ADDR. This change ensures that the MPTCP path manager properly cleans up ADD_ADDR announcements.

Defensive priority

Verify and apply kernel updates to ensure MPTCP path manager is properly cleaning up ADD_ADDR announcements.

Recommended defensive actions

• Verify kernel version and apply updates if necessary
• Review system configurations for MPTCP path manager
• Monitor system logs for WARN_ON_ONCE(mptcp_pm_is_kernel()) errors
• Perform a thorough review of system configurations and MPTCP path manager settings
• Check for any exposed assets that may require extra review
• Track exceptions and retest remediated assets
• Document evidence of remediation

Evidence notes

The CVE record and source references indicate a vulnerability in the Linux kernel's MPTCP path manager. However, details on exploitation, impact, and remediation are limited. Defenders should verify kernel versions, review system configurations, and monitor system logs for potential issues. The source provides a brief description of the vulnerability and its resolution, but further analysis is needed to fully understand the vulnerability's impact.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.