CVE-2026-99229 is a Linux kernel vulnerability in the io_uring subsystem where a task can spin indefinitely on a stuck overflow list. This occurs because io_cqring_wait_schedule() returns early when IO_CHECK_CQ_OVERFLOW_BIT is set, preventing proper flushing of the overflow list and causing the task to spin in the kernel without responding to signals, including SIGKILL. The issue arises especially with IORING_SETUP_CQE_MIXED and when the application manipulates the completion queue head, leading to a stuck state that cannot be interrupted.