CVE-2026-74653
Received Received - Intake

Interrupt Storm in Linux Kernel LPC32xx UART Driver

Publication date: 2026-08-22

Last updated on: 2026-08-22

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx The NXP LPC32xx UART (PORT_LPC3220) can latch an RX character-timeout interrupt while the RX FIFO is empty: IIR reports UART_IIR_RX_TIMEOUT (0x0c) but LSR.DR is clear. A character timeout is only cleared by reading RHR, but serial8250_rx_chars() reads RHR only when LSR.DR is set, so nothing ever clears the condition. The interrupt is level-triggered and re-fires immediately, so on a single-core ARM926 the resulting interrupt storm livelocks the CPU. It is reproducible when userspace repeatedly opens the front-panel port (ttyS1): serial8250_do_set_termios() re-enables interrupts on unlock and the handler then spins forever with iir=0xcc lsr=0x60 ier=0x05, tripping the soft-lockup detector in serial8250_handle_irq_locked(). LPC32xx has no dedicated 8250 glue driver, it's driven by the generic 8250_of. Add a hardware specific handle_irq for PORT_LPC3220, wired up in of_platform_serial_setup() the same way fsl8250_handle_irq is installed. The handler follows dw8250_handle_irq(): on an RX timeout with an empty FIFO (LSR.DR and LSR.BI clear) it does one throwaway RHR read to clear the condition, then calls serial8250_handle_irq_locked(). No real received data is ever discarded, and it is a no-op on healthy UARTs which never report a timeout with DR clear. This is the same class of bug already worked around in other 8250 drivers; see commit 424d79183af0 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt") which reports the identical iir=0xcc/lsr=0x60. See also UART_RX_TIMEOUT_QUIRK in 8250_omap, and the note in 8250_bcm7271.

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Meta Information

Published
2026-08-22
Last Modified
2026-08-22
Generated
2026-08-22
AI Q&A
2026-08-22
EPSS Evaluated
N/A
NVD
CVE-2026-74653
EUVD
EUVD-2026-64590

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
nxp lpc32xx *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability affects the NXP LPC32xx UART in the Linux kernel. It causes a stuck RX-timeout interrupt when the RX FIFO is empty, leading to an interrupt storm that livelocks the CPU. The issue occurs because the interrupt is not cleared properly, causing repeated firings.

Detection Guidance

This vulnerability is specific to the NXP LPC32xx UART hardware and requires kernel-level detection. Check if your system uses the PORT_LPC3220 UART by examining kernel logs for UART_IIR_RX_TIMEOUT errors or CPU soft-lockup messages during serial port activity.

Impact Analysis

The vulnerability can cause system instability by triggering an interrupt storm, which may freeze or severely degrade performance on affected systems. It is particularly problematic on single-core ARM926 systems using the LPC32xx UART port.

Mitigation Strategies

Apply the Linux kernel patch that adds a hardware-specific handle_irq for PORT_LPC3220. Update to a kernel version containing the fix or backport the patch manually. Avoid opening the affected serial port repeatedly in userspace until patched.

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