CVE-2026-97566 mptcp: pm: kernel: drop pending ADD_ADDR when removing ID0
A logic error in the Linux kernel MPTCP path manager causes a kernel warning and potential denial of service when removing the ID0 endpoint.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-97566?
CVE-2026-97566 is a denial of service vulnerability in Linux, published on 25 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-97566?
How do I fix CVE-2026-97566?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-97566 being exploited?
There is no known exploitation of CVE-2026-97566 in the wild and no public exploit code.
Sources
Also known as AZL-104667, BELL-CVE-2026-97566, DEBIAN-CVE-2026-97566, GHSA-27x2-682m-9qm4, UBUNTU-CVE-2026-97566.