CVE-2026-64119
In the Linux kernel, the following vulnerability has been resolved: l2tp: use list_del_rcu in l2tp_session_unhash An unprivileged local user can pin a host CPU indefinitely in l2tp_session_get_by_ifname() by issuing L2TP_CMD_SESSION_GET on L2TP_ATTR_IFNAME concurrently with L2TP_CMD_SESSION_CREATE and L2TP_CMD_SESSION_DELETE on the same tunnel. All three commands take GENL_UNS_ADMIN_PERM, so CAP_NET_ADMIN in the netns user namespace suffices; on any host that has l2tp_core loaded the trigger is reachable from a standard `unshare -Urn` sandbox. l2tp_session_unhash() removes a session from tunnel->session_list with list_del_init(), but that list is walked by l2tp_session_get_by_ifname() with list_for_each_entry_rcu() under rcu_read_lock_bh(). list_del_init() leaves the deleted entry's next/prev self-pointing; a reader that has loaded the entry and then advances pos->list.next reads &session->list, container_of()s back to the same session, and list_for_each_entry_rcu() never reaches the list head. The CPU stays in strcmp() inside the walker, with BH and preemption disabled, so RCU grace periods on the host stall behind it and the wedged thread cannot be killed (SIGKILL is delivered
No public exploitation has been reported so far. No distribution fix is listed yet; apply vendor mitigations and monitor.
Recommended action: Track your distribution's security tracker and apply the fix as soon as it ships.
Affected & fixed versions by distribution
Versions are the native distribution strings (backport-aware): RHEL/Debian/SUSE backport fixes, so compare with the distro version comparator (dpkg / rpm / vercmp), not the upstream version.
No affected package in the tracked watchlist yet (Debian, Ubuntu, Arch, SUSE, Red Hat...). Triage may still be pending.