From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97481][LOW] serial: 8250: fix possible ISR soft lockup [ Upstream Date: Thu, 24 Sep 2026 19:23:14 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97481 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: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 2881b2e6da02daea1eb8254247ba8fd20c9d3348 List-Id: CVE: CVE-2026-97481 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: serial: 8250: fix possible ISR soft lockup [ Upstream Commit: 2881b2e6da02daea1eb8254247ba8fd20c9d3348 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2881b2e6da02daea1eb8254247ba8fd20c9d3348 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97481 Analysis date: Thu, 24 Sep 2026 19:23:14 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97481 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97481 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-2026-97481 LOW https://www.kernelcve.org/list/?q=CVE-2026-97481 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-754;BEST CVSS score: '4.2';DESCR 'An unhandled FIFO error interrupt in the 8250 serial driver can repeatedly retrigger when FIFO error is set but no data ready status is present. This can trap a CPU in the UART interrupt handler and cause a soft lockup or system level denial of service. For the CVSS the PR:N value is used because an attacker with physical control of the affected UART line or connected serial device does not need local code execution on the target. The attack is not network reachable and requires rare hardware and timing conditions during serial startup. Impact is limited to availability because the patch indicates no memory corruption information disclosure or privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES DEADLOCK INIT PRINTF-TTY SIMPLEFIX HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: -2 * Conservative score: 0 * Raw paranoid score: -2 * Paranoid score: 0 * Applied score floor: -2 -> 0. The score cannot be negative. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel soft lockup / strong DoS. The commit describes the host becoming stuck in the UART ISR because the same unhandled FIFO error interrupt is immediately retriggered. * -1 Hard or unreliable timing condition. The commit explicitly describes rare cases during the serial startup phase and requires the FIFO error condition without data ready status. * -2 Physical-only access requirement. Triggering requires control of the affected UART line or a connected serial device. No direct network, syscall, or ordinary local-user trigger is established. * No memory-corruption signal awarded. The patch only clears and reinitializes the FIFO after an unhandled hardware status combination. * No UAF, stale pointer, double free, refcount mutation, OOB access, arbitrary write, disclosure, authorization bypass, or ownership violation is established. * No extra Availability point awarded. The ISR soft lockup is the same consequence already counted by the Reliable kernel soft lockup signal. * No remote reachability bonus awarded. The vulnerable condition is produced through UART hardware input and interrupt behavior, not network traffic. * No subsystem rarity penalty was separately applied. The physical-only reduction already captures the material access restriction and must not be double-counted. 3. Reachability analysis The evaluated attacker is a person or device with physical control of the affected UART interface or an attached serial peripheral. Such an attacker may be able to flood the UART during startup and create the FIFO error interrupt condition without executing code on the host. Host administrator privileges are not required once the attacker has the required physical serial access. This supports HostAdminRequired=NO, but does not make the issue remotely reachable or locally reachable through an ordinary userspace interface. The complete trigger is not namespace-scoped. Network namespaces, containers, delegated capabilities, or user namespaces do not provide the required UART hardware-line control. No prior privileged software setup is established by the patch, although practical exploitation requires that an affected UART interface is present, active, and externally controllable. 4. Primitive and severity interpretation The primitive is an interrupt-handling logic failure. When UART_LSR_FIFOE is set while UART_LSR_DR is clear, the driver previously returned IRQ_HANDLED without clearing the FIFO error condition. The interrupt controller can then immediately deliver the same interrupt again, trapping a CPU in serial8250_handle_irq_locked and causing an ISR soft lockup. This is CLASS_C because the demonstrated effect is invalid device state handling and denial of service. It is not an active structured-object lifetime issue, fixed stale storage issue, UAF, reference-count defect, or memory-corruption primitive. The demonstrated consequence is a CPU soft lockup and possible host-level availability degradation. The patch does not establish controlled memory access, attacker-controlled kernel object reuse, confidentiality impact, integrity impact, privilege escalation, or persistent cross-boundary impact. ImportantCandidate=NO because the available evidence supports a constrained physical DoS only. AutoDowngradeAllowed=YES because no unresolved kernel corruption, security-boundary bypass, or meaningful exploitation primitive remains. 5. One-sentence report phrase A physically connected UART device may trigger a rare FIFO error interrupt condition during startup, causing repeated 8250 ISR execution and a host soft lockup, with impact limited to denial of service. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a hardware-input-dependent ISR livelock without memory corruption, authorization bypass, or privilege-escalation evidence. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: serial: 8250: fix possible ISR soft lockup [ Upstream Commit: 2881b2e6da02daea1eb8254247ba8fd20c9d3348 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2881b2e6da02daea1eb8254247ba8fd20c9d3348 Changed files: drivers/tty/serial/8250/8250_port.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=2881b2e6da02daea1eb8254247ba8fd20c9d3348 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97481 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97481 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:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.2 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: 0 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).