CVE-2026-12631 Broken access-control denial in k_thread_join/k_thread_abort syscall validation in Zephyr kernel

The Zephyr kernel validates the kthreadjoin and kthreadabort system calls declared syscall in include/zephyr/kernel.h through threadobjvalidate in kernel/thread.c. Its default switch branch is the access-denied path, taken when kobjectvalidate returns -EPERM the calling user thread was never...