From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74653][LOW] serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx Date: Sat, 22 Aug 2026 11:52:28 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74653 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 3ce24bc4d115336218e59b7e286fd3a79f4fc4c6 List-Id: 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 Assisted-by: Claude:Opus4.8 Signed-off-by: Ryan Wilbur Link: https://patch.msgid.link/20260730193920.28954-1-rwilbur633@gmail.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman 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).