CVE-2026-97566

Published Sep 25, 2026

Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: kernel: drop pending ADD_ADDR when removing ID0 The in-kernel MPTCP path manager can leave a stale ADD_ADDR announcement entry alive when removing the id 0 endpoint. This happens because the id 0 removal path does not tear down pending announcements, unlike the non-zero id path. When the PM later reselects id 0 after adding another signal endpoint, it finds the stale anno_list entry and hits WARN_ON_ONCE(mptcp_pm_is_kernel()) in mptcp_pm_announced_alloc(). Root cause: asymmetry between removal paths. - Non-zero id path: mptcp_nl_remove_subflow_and_signal_addr() calls mptcp_pm_remove_announced() to clean up. - Id 0 path: mptcp_nl_remove_id_zero_address() skips cleanup entirely. Fix by making the id 0 path symmetric: call mptcp_pm_announced_remove() and decrement add_addr_signaled before queuing the RM_ADDR. Subtle detail: signal endpoints are stored in anno_list with port 0, but msk_local carries the connection's local port. In other words, entries linked to ID0 paths should have port == 0. A follow-up patch will ensure that. mptcp_pm_announced_remove() uses use_port=true for comparison. So clear the port before the lookup.

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References

Frequently Asked Questions

What is CVE-2026-97566? +
In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: kernel: drop pending ADD_ADDR when removing ID0 The in-kernel MPTCP path manager can leave a stale ADD_ADDR announcement entry alive when removing the id 0 endpoint. This happens because the id 0 removal path does not tear down pending announcements, unlike the non-zero id path. When the PM later reselects id 0 after adding another signal endpoint, it finds the stale anno_list entry and hits WARN_ON_ONCE(mptcp_pm_is_kernel()) in mptcp_pm_announced_alloc(). Root cause: asymmetry between removal paths. - Non-zero id path: mptcp_nl_remove_subflow_and_signal_addr() calls mptcp_pm_remove_announced() to clean up. - Id 0 path: mptcp_nl_remove_id_zero_address() skips cleanup entirely. Fix by making the id 0 path symmetric: call mptcp_pm_announced_remove() and decrement add_addr_signaled before queuing the RM_ADDR. Subtle detail: signal endpoints are stored in anno_list with port 0, but msk_local carries the connection's local port. In other words, entries linked to ID0 paths should have port == 0. A follow-up patch will ensure that. mptcp_pm_announced_remove() uses use_port=true for comparison. So clear the port before the lookup.
How do I check if I'm vulnerable to CVE-2026-97566? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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