From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99216][LOW] Drivers: hv: Don't reset VMBus connection state on error/exit paths [ Upstream Date: Fri, 30 Oct 2026 10:54:38 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99216 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: 2 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: f47ce27af80b87cc684d5c12b65506af498ac7e5 List-Id: CVE: CVE-2026-99216 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: Drivers: hv: Don't reset VMBus connection state on error/exit paths [ Upstream Commit: f47ce27af80b87cc684d5c12b65506af498ac7e5 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f47ce27af80b87cc684d5c12b65506af498ac7e5 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99216 Analysis date: Fri, 30 Oct 2026 10:54:38 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: Prematurely marking VMBus disconnected can suppress actual connection teardown and leave host messages or interrupts active during guest cleanup, with disruption possible but no demonstrated memory corruption or panic. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99216 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99216 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-2026-99216 LOW https://www.kernelcve.org/list/?q=CVE-2026-99216 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-404;CWE-459;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A VMBus lifecycle logic error marks the connection as DISCONNECTED before vmbus_disconnect checks whether an active connection must be unloaded. This can leave the Hyper V connection active after a connection failure or during driver exit, allowing the host to continue sending messages or posting VMBus interrupts while guest cleanup is in progress. The demonstrated primitive is incomplete teardown and continued asynchronous activity rather than a proven UAF, OOB access, or arbitrary write. For the CVSS the PR:N value in the paranoid vector reflects that a Hyper V host can generate VMBus events without privileges inside the guest once the guest enters the affected cleanup path. AC:H reflects the required error or exit state and the unresolved timing between host events and guest teardown. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE INIT LEAK LINUS KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 1. * Conservative score: 1; no floor or cap applied. * Raw paranoid score: 2. * Paranoid score: 2; no floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * **+1 weak/indirect lifecycle-state defect:** setting `conn_state` to `DISCONNECTED` causes `vmbus_initiate_unload()` to skip unloading an actually remaining connection. Host messages or interrupts may therefore continue during cleanup. * **Paranoid +1 availability concern:** continued asynchronous host activity after guest teardown begins plausibly permits guest disruption. The patch does not establish a reliable panic, so this is retained only in the paranoid score. * No UAF, OOB access, repeated release, refcount mutation, arbitrary write, controlled reclaim, disclosure, or authorization bypass is shown. * No extra crash or availability point is awarded: a host-wide crash is not demonstrated. * B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of corrupted heap state. * B3-PENDING does not apply: no shared-backing write exists. * B4-PENDING does not apply: the connection-state check is a lifecycle guard, not an authorization DENY-to-ALLOW decision. 3. Reachability analysis The vulnerable paths are VMBus connection-failure cleanup and driver exit. A Hyper-V host can continue generating VMBus messages or interrupts after the guest reaches either path, but the evidence does not show that an attacker can independently force the complete failure/exit sequence. Driver exit may require privileged guest administration, while connection failure may be host-influenced; the supplied evidence does not resolve this split. No namespace-scoped trigger is shown. Hyper-V virtualization is required, but no rarity penalty is applied. 4. Primitive and severity reading The exact primitive is incomplete retirement of an active VMBus connection caused by prematurely changing its state before the disconnect routine checks it. This is invalid active-state/teardown behavior, classified as **CLASS_C**, not a demonstrated memory-lifetime violation. The shown consequence is continued host-to-guest asynchronous activity; guest panic, stale-memory access, corruption, or escape remains unproven. Consequently, there is no Important-class primitive and automatic downgrade remains allowed. 5. One-sentence report phrase Prematurely marking VMBus disconnected can suppress actual connection teardown and leave host messages or interrupts active during guest cleanup, with disruption possible but no demonstrated memory corruption or panic. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether host-driven messages can reach handlers after their supporting guest state is destroyed or cause a reproducible guest-wide failure. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: Drivers: hv: Don't reset VMBus connection state on error/exit paths [ Upstream Commit: f47ce27af80b87cc684d5c12b65506af498ac7e5 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f47ce27af80b87cc684d5c12b65506af498ac7e5 Changed files: drivers/hv/connection.c 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=f47ce27af80b87cc684d5c12b65506af498ac7e5 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99216 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99216 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: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.3 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: 1 Paranoid ActionableScore: 2 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).