The NXP LPUART serial driver (drivers/serial/uartmcuxlpuart.c), when CONFIGUARTUSERUNTIMECONFIGURE is enabled, called LPUARTDeinit() at the start of mcuxlpuartconfigure(), which disables the LPUART peripheral clocks. The requested configuration is validated only afterwards (in mcuxlpuartconfigurebasic), and unsupported parity/data-bit/stop-bit/flow-control values return -ENOTSUP before the clock is re-enabled.

As a result, a uartconfigure() request with an unsupported configuration left the LPUART in a clock-disabled state; any subsequent access to LPUART registers (pollout/pollin, interrupt handling, or a later reconfigure) faults on the gated peripheral and escalates to a hard fault, crashing the system.

uartconfigure() is a Zephyr syscall whose verifier (zvrfyuartconfigure) only checks that cfg is readable user memory and forwards the caller-supplied configuration unchanged, so an unprivileged userspace thread with access to an LPUART device can deterministically trigger the fault, a persistent system-wide denial of service.

Introduced in v2.5.0 and present in all subsequent releases until this fix, which removes the LPUARTDeinit() call and instead only disables the transmitter/receiver, leaving the clock running.