The ARM PL011 UART driver in Zephyr fails to acknowledge error interrupts due to a missing write to the interrupt-clear register. When an application enables error‑interrupt reporting, an external peer can inject framing, parity, break, or overrun errors, keeping the interrupt line asserted. The kernel repeatedly calls the ISR, creating a livelock that permanently hangs the core. The flaw is a classic case of uncontrolled resource consumption, classified as CWE‑835, and results in an availability‑only denial of service.

Zephyr RTOS, particularly builds that use the PL011 UART driver and call uart_irq_err_enable() to enable error interrupts. The exact affected versions are not listed, so any Zephyr release prior to the commit that introduces the fix is potentially vulnerable.

With a CVSS score of 4.6, the vulnerability is of moderate severity. EPSS information is not available, and it is not yet listed in the CISA KEV catalog. Exploitation requires physical or remote communication with the external UART peer and the application must have explicitly enabled error interrupts; thus the attack vector is likely local physical or removable UART access. Given the control an attacker has over the UART line, the risk of service disruption is tangible but mitigated by the fact that error interrupts are disabled by default and no standard Zephyr subsystem enables them.