[CVE-2026-74653][LOW] serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx

[CVE-2026-74653][LOW] serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx

[AL-KERNEL]

CVE: CVE-2026-74653
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx
Commit: 3ce24bc4d115336218e59b7e286fd3a79f4fc4c6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ce24bc4d115336218e59b7e286fd3a79f4fc4c6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74653
Analysis date: Sat, 22 Aug 2026 11:52:28 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74653 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74653

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-74653	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-400;*CWE-835;CWE-754;BEST CVSS score: '5.5';DESCR 'The LPC32xx 8250 UART can report an RX timeout interrupt while the RX FIFO is empty. The core serial8250 RX path only reads RHR when LSR DR is set, so the timeout condition is not cleared and the level triggered interrupt can immediately re fire forever. A local user or process that can open the affected tty device can trigger repeated interrupt handling and CPU livelock on the affected single core LPC32xx system. For the CVSS the PR:L is used because reliable triggering requires local access to the tty device, commonly through a user session or a delegated device permission rather than full administrator privileges. The issue is not network reachable. Impact is denial of service through CPU livelock or soft lockup, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	DEADLOCK PRINTF-TTY DMAorINTERRUPT HARDWARE LINUS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	guess

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**

2. Signal breakdown
* Local unprivileged trigger: +1. A local user or process with access to the affected tty device can repeatedly open the port and trigger the condition.
* Reliable kernel crash / strong DoS: +1. The commit describes a reproducible interrupt storm and CPU livelock on single-core LPC32xx systems.
* Availability impact realistic: +1. The livelock can effectively stall the affected system CPU until the interrupt condition is cleared or the system is recovered.
* Physical-only or rare hardware-only condition: -2. The issue is specific to NXP LPC32xx UART hardware using PORT_LPC3220 through 8250_of.
* No memory corruption signal. The patch only clears a stuck hardware interrupt condition with a throwaway RHR read.
* No privilege escalation signal. There is no UAF, OOB write, refcount issue, stale callback, object confusion, or attacker-controlled memory primitive.

3. Reachability analysis
The bug is locally triggerable by code that can open the affected serial tty device. It is not network reachable. Namespace or container exposure depends on whether the tty device is delegated into the container, but this does not create a broader kernel memory corruption primitive. The affected path is hardware-specific and requires LPC32xx UART behavior, so exposure is narrow and not common on general Linux systems.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like hardware-specific DoS issue. The realistic impact is CPU livelock or soft lockup on affected LPC32xx systems. The theoretical impact does not extend to confidentiality, integrity, or privilege escalation based on the patch because the fix addresses interrupt clearing logic only.

5. One-sentence report phrase
A hardware-specific LPC32xx 8250 UART RX-timeout quirk can leave a level-triggered interrupt uncleared when the FIFO is empty, allowing a local tty user to cause CPU livelock and denial of service.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The issue is a narrow hardware-specific local DoS with no supported memory corruption, privilege escalation, or network-triggerable primitive.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx
Commit: 3ce24bc4d115336218e59b7e286fd3a79f4fc4c6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ce24bc4d115336218e59b7e286fd3a79f4fc4c6

Commit description:

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 424d791 ("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.

Cc: stable <stable@kernel.org>
Assisted-by: Claude:Opus4.8
Signed-off-by: Ryan Wilbur <rwilbur633@gmail.com>
Link: https://patch.msgid.link/20260730193920.28954-1-rwilbur633@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/tty/serial/8250/8250_of.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ce24bc4d115336218e59b7e286fd3a79f4fc4c6

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74653 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74653

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: unknown
  Paranoid ActionableScore: 1

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).