From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90097][LOW] Drivers: hv: vmbus: Skip VMBus module cleanup for non-nested root partition [ Upstream Date: Fri, 18 Sep 2026 04:57:11 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90097 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: aa17842bbccaeaba7d05c166019d1c96a41bca54 List-Id: CVE: CVE-2026-90097 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: Drivers: hv: vmbus: Skip VMBus module cleanup for non-nested root partition [ Upstream Commit: aa17842bbccaeaba7d05c166019d1c96a41bca54 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa17842bbccaeaba7d05c166019d1c96a41bca54 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90097 Analysis date: Fri, 18 Sep 2026 04:57:11 -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-2026-90097 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90097 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-2026-90097 LOW https://www.kernelcve.org/list/?q=CVE-2026-90097 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:H/UI:N/S:U/C:N/I:N/A:H';CWE-665;CWE-754;**CWE-476;BEST CVSS score: '4.4';DESCR 'VMBus can be loaded in a non-nested Hyper-V root partition even though hv_acpi_init skips the real VMBus initialization. If the module is later unloaded, vmbus_exit may try to clean up SynIC and related VMBus state that was never initialized, which can cause memory faults and a kernel panic. For the CVSS the PR:H value is used because reliable triggering normally requires the ability to unload a kernel module, which is an administrative operation requiring CAP_SYS_MODULE or equivalent host control. The issue is not network reachable and is tied to local module lifecycle management on a specific Hyper-V root partition configuration. Impact is denial of service only via host kernel crash.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES DANGER INIT 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=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 0 * Conservative score: 0 * Raw paranoid score: 0 * Paranoid score: 0 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap changed the score. 2. Signal breakdown Positive signals: * +1 Reliable kernel crash / strong DoS. The commit states that unloading the module can result in memory faults and a panic. * +1 Concrete invalid initialization / cleanup state mismatch. hv_acpi_init can report success without performing VMBus initialization, while vmbus_exit later assumes initialized VMBus state exists. Negative signals: * -2 Host-admin-equivalent privilege required. Reliable triggering requires unloading a kernel module, which normally requires host root or CAP_SYS_MODULE. Important non-awarded signals: * Real UAF not awarded. The patch shows cleanup of uninitialized state, not a post-free stale object use. * Concrete repeated release/refcount not awarded. No first release plus surviving exact reference plus second lifetime mutation is established. * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Confidentiality and integrity impact not awarded. * Remote reachability not established. * Extra availability point not awarded because the panic is the same DoS consequence already counted. * ImportantCandidate not awarded because the demonstrated primitive is host-admin-triggered crash-only invalid cleanup. 3. Reachability analysis The trigger is local module lifecycle management on a non-nested Hyper-V root partition. The relevant operation is VMBus module unload after the module was loaded successfully even though initialization was skipped. This is host-admin-equivalent in normal Linux deployments because module unload requires CAP_SYS_MODULE or equivalent host control. No namespace-scoped complete trigger is established. No network trigger is established. The configuration is specific to Hyper-V root partition behavior, but no separate rare-hardware penalty is needed because the host-admin requirement already captures the practical restriction. There is no race requirement. 4. Primitive and severity interpretation The primitive is invalid cleanup of never-initialized kernel state. It is not an active structured UAF and not fixed stale storage after free. The demonstrated consequence is memory fault and kernel panic during module unload. The speculative consequence would be broader memory corruption, but the supplied patch does not establish UAF, double free, refcount corruption, controlled reclaim, directed write, callback control, or security-boundary bypass. PrimitiveClass is CLASS_C because the evidence supports crash/DoS behavior without an independently useful corruption primitive. ImportantCandidate is NO because host-admin triggering and crash-only impact leave no meaningful Important-vs-Moderate exploitation leverage unresolved. AutoDowngradeAllowed is YES. 5. One-sentence report phrase VMBus module unload in a non-nested Hyper-V root partition can attempt cleanup of state that was never initialized, causing a host kernel panic, but reliable triggering requires host-admin module unload privileges. 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: host-admin-only module unload path, no UAF or repeated lifetime mutation, no C/I impact, no network reachability, and demonstrated impact is DoS only. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: Drivers: hv: vmbus: Skip VMBus module cleanup for non-nested root partition [ Upstream Commit: aa17842bbccaeaba7d05c166019d1c96a41bca54 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa17842bbccaeaba7d05c166019d1c96a41bca54 Changed files: drivers/hv/vmbus_drv.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=aa17842bbccaeaba7d05c166019d1c96a41bca54 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90097 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90097 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:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.4 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).