From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98466][IMPORTANT] KVM: arm64: Transfer the hyp stack pages out of the host stage-2 Date: Sat, 24 Oct 2026 09:23:04 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98466 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: e5dd2a91a7ae3a276e6d79806127e923936e241b List-Id: CVE: CVE-2026-98466 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: KVM: arm64: Transfer the hyp stack pages out of the host stage-2 Commit: e5dd2a91a7ae3a276e6d79806127e923936e241b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e5dd2a91a7ae3a276e6d79806127e923936e241b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98466 Analysis date: Sat, 24 Oct 2026 09:23:04 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: Incomplete pKVM ownership transfer leaves protected hypervisor stack pages accessible through the compromised host’s stage-2 mapping. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98466 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98466 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: IMPORTANT Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98466 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98466 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H';CWE-284;CWE-668;CWE-276;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:C/C:L/I:H/A:H';BEST CVSS score: '8.2';DESCR 'The pKVM host ownership setup omitted per-CPU hypervisor stack pages because those stacks use private virtual addresses and have no linear-map alias visited by fix_host_ownership. As a result the pages could remain accessible through the host stage-2 and a compromised host kernel could potentially inspect sensitive hypervisor stack contents, modify control or data values, or corrupt a stack to crash or influence protected hypervisor execution. For the CVSS the PR:H value is used because reliable exploitation requires host kernel level control rather than ordinary access to a KVM device or execution inside a guest. The issue crosses the intended host to protected hypervisor isolation boundary. It is local and limited to arm64 protected nVHE pKVM configurations. No UAF, OOB access, direct guest trigger, or network reachability is demonstrated. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 8.2 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 6.1 and ActionableScore 5 with primitive class CLASS_A and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE VIRT INIT SIMPLEFIX HARDWARE LINUS INCREASED_TO_HIGH_BASED_ON_GUESSCVSS TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=CONFIRMED B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 5. * Conservative score: 5; no floor or cap applied. * Raw paranoid score: 5. * Paranoid score: 5; stronger execution-control claims would require unsupported assumptions. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2: Strong protected-memory ownership primitive. The omitted walk leaves per-CPU hypervisor stack pages in the host stage-2 instead of transferring them out of host ownership. * +2: Concrete pKVM isolation-boundary failure. A compromised host kernel retains access to memory intended to be private to the protected hypervisor. * +1: Confidentiality plausible because the retained mapping can expose hypervisor stack contents. * +1: Integrity plausible because host access can modify live hypervisor stack state. * -1: Exposure requires arm64 protected-nVHE pKVM and its guarded private-VA stacks, a materially specialized configuration. * No host-admin penalty: host-kernel control is required, but the defect defeats an additional host-to-protected-hypervisor boundary. * No UAF, OOB write, controlled reclaim, ordinary guest trigger, network reachability, or demonstrated code execution. * No extra availability point: stack corruption could plausibly crash protected execution, but no reliable crash path is shown. 3. Reachability analysis The supported attacker is a compromised or malicious host kernel, not an ordinary guest, `/dev/kvm` user, namespace-capable process, or normal local user. Host-admin-equivalent control is therefore required. Numeric host UID 0 is not independently established as either necessary or sufficient. No namespace-scoped trigger, special race, retry sequence, or guest-only invocation is shown. Prior activation of arm64 protected nVHE pKVM is required. 4. Primitive and severity reading The primitive is retained host stage-2 access to active, protected hypervisor stack pages due to incomplete ownership transfer. This is fixed live structured storage, not a UAF or retry-accumulated OOB write. The patch directly establishes the ownership omission; normal pKVM semantics support host access to pages left in the host stage-2. Protected hypervisor memory exposure is confirmed, while extraction of particular secrets, controlled stack corruption, host-to-hypervisor code execution, and guest escape remain unproven. This is CLASS_A because it compromises the explicit host/hypervisor memory-isolation boundary. ImportantCandidate is YES and auto-downgrade is disallowed despite the powerful attacker prerequisite. This is not B4-PENDING: no authorization predicate changes DENY to ALLOW at an attacker-invocable interface. 5. One-sentence report phrase Incomplete pKVM ownership transfer leaves protected hypervisor stack pages accessible through the compromised host’s stage-2 mapping. 6. Manual review advice MANUAL CHECK REQUIRED Confirm the effective host-stage-2 permissions and whether stack contents or control data are practically readable or writable in affected pKVM configurations. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: arm64: Transfer the hyp stack pages out of the host stage-2 Commit: e5dd2a91a7ae3a276e6d79806127e923936e241b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e5dd2a91a7ae3a276e6d79806127e923936e241b Commit description: fix_host_ownership() walks only the linear-map alias of each memblock region, and the per-CPU hyp stack, mapped in the private VA range for its guard page, has none. Walk each stack's VA range with the same walker. Fixes: 1a919b1 ("KVM: arm64: Add guard pages for pKVM (protected nVHE) hypervisor stack") Reported-by: Hiroyuki Katsura Cc: stable@vger.kernel.org Signed-off-by: Fuad Tabba Reviewed-by: Vincent Donnefort Tested-by: Vincent Donnefort Reviewed-by: Marc Zyngier Link: https://patch.msgid.link/20260908110713.1540304-2-fuad.tabba@linux.dev Signed-off-by: Oliver Upton Signed-off-by: Greg Kroah-Hartman Changed files: arch/arm64/kvm/hyp/nvhe/setup.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=e5dd2a91a7ae3a276e6d79806127e923936e241b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98466 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98466 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:C/C:L/I:H/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H The Best / paranoid CVSS score: 8.2 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: 5 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: IMPORTANT KPANIC detected for this report: NO Published priority for this report (same as in Subject): IMPORTANT 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).