From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89931][MODERATE REGULAR] KVM: nVMX: Ensure KVM_REQ_GET_NESTED_STATE_PAGES is cleared on VM-Exit Date: Wed, 16 Sep 2026 13:37:52 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89931 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: ae190f2439ca30067927077bf570d4c5edf07a0f List-Id: CVE: CVE-2026-89931 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: KVM: nVMX: Ensure KVM_REQ_GET_NESTED_STATE_PAGES is cleared on VM-Exit Commit: ae190f2439ca30067927077bf570d4c5edf07a0f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae190f2439ca30067927077bf570d4c5edf07a0f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89931 Analysis date: Wed, 16 Sep 2026 13:37:52 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89931 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89931 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: MODERATE REGULAR 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-2026-89931 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89931 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-665;*CWE-672;*CWE-772;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'KVM nVMX may fail to clear KVM_REQ_GET_NESTED_STATE_PAGES when CONFIG_KVM_HYPERV is disabled because the request check was compiled only under the Hyper V path. A nested guest workflow can then leave the request pending across a nested VM Exit and later VMLAUNCH or VMRESUME, which may double map vmcs12 related pages. For the CVSS the PR:L is used because an attacker needs local ability to use KVM and run a nested virtualization workload, but full host administrative privileges are not necessarily required in common /dev/kvm group based deployments. The issue is not network reachable and is triggered through local KVM ioctls and guest execution rather than packet traffic. Impact is primarily denial of service or resource exhaustion from repeated page mapping or reference retention. No concrete arbitrary write, UAF, or information leak primitive is visible from this patch, so confidentiality and integrity remain none for the grounded score.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE DANGER VIRT SIMPLEFIX HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2. No floor or cap applied. * Raw paranoid score: 3 * Paranoid score: 3. No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Positive signals: * +1. Stale KVM request state can survive VM Exit when CONFIG_KVM_HYPERV is disabled. The patch explicitly says KVM relies on kvm_check_request to clear KVM_REQ_GET_NESTED_STATE_PAGES. * +1. Concrete KVM nested state mapping inconsistency is established. The uncleared request may lead to double mapping of vmcs12 pages. * +1 paranoid only. Repeated double mapping can plausibly create resource or reference retention and host KVM instability, but the patch does not prove a stronger corruption primitive. Negative or non-awarded signals: * No RealUAF awarded. The supplied patch does not establish use after free or stale post lifetime object dereference. * No concrete repeated release or refcount mutation is established. There is no visible first put followed by a second put on the exact same dangling reference. * No controlled reclaim, arbitrary write, directed host memory corruption, callback control, or information leak is demonstrated. * No KVM guest to host strong exploitation leverage awarded. The bug is in host KVM state, but the patch only establishes uncleared request state and possible double mapping. * No remote reachability awarded. This is not packet reachable. * No race penalty applied. The issue is an ordered stale request clearing bug, not a proven narrow timing race. * No rare hardware penalty applied. Nested VMX and KVM are configuration dependent, but the supplied evidence does not prove rare physical hardware or physical access. 3. Reachability analysis The evaluated attacker is a local VMM or local host user with access to /dev/kvm and ability to run nested virtualization workloads. A malicious guest may participate by causing nested VM Entry or VM Exit sequences, but the supplied evidence does not prove that a guest only attacker can complete the full trigger without cooperation from the VMM or host userspace. Host administrator privilege is not positively required because KVM is commonly exposed to non root users through /dev/kvm group access. This is still not ordinary remote reachability and not namespace scoped privilege. No network namespace, CAP_NET_ADMIN, BPF, or container scoped capability path is involved. Prior KVM availability and nested virtualization support are prerequisites. CONFIG_KVM_HYPERV=n is the relevant affected build condition. No special physical hardware beyond KVM capable x86 virtualization is established. Race repeatability is not the key issue. 4. Primitive and severity interpretation The exact primitive is stale request state in KVM nVMX: KVM_REQ_GET_NESTED_STATE_PAGES may remain pending because the request check was compiled only under CONFIG_KVM_HYPERV. Since kvm_check_request also clears the request, skipping it can allow later nested VMLAUNCH or VMRESUME paths to process the same nested state page mapping request again. This is best classified as CLASS_C invalid state or resource mapping behavior. It is not a demonstrated UAF, not a concrete double release, and not a proven active structured stale object reuse. The demonstrated consequence is possible double mapping of vmcs12 pages and likely DoS or resource instability. Stronger consequences such as guest to host memory corruption or privilege escalation are speculative from this patch alone. ImportantCandidate=NO because no Class A primitive and no sufficiently strong Class B lifetime corruption primitive is established. AutoDowngradeAllowed=YES because the evidence supports borderline manual review for KVM state handling, but not an unresolved Important grade exploitation primitive. 5. One-sentence report phrase KVM nVMX may fail to clear KVM_REQ_GET_NESTED_STATE_PAGES on nested VM Exit when CONFIG_KVM_HYPERV is disabled, allowing a local VMM attacker with /dev/kvm access to trigger possible double mapping of vmcs12 pages and host DoS or resource instability. 6. Manual review recommendation MANUAL CHECK RECOMMENDED KVM nested state page mapping is security sensitive and should be checked manually, but the supplied patch does not establish UAF, arbitrary host memory access, guest to host escape, or privilege escalation. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: nVMX: Ensure KVM_REQ_GET_NESTED_STATE_PAGES is cleared on VM-Exit Commit: ae190f2439ca30067927077bf570d4c5edf07a0f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae190f2439ca30067927077bf570d4c5edf07a0f Commit description: Always check and clear KVM_REQ_GET_NESTED_STATE_PAGES when emulating a nested VM-Exit to ensure the request is cleared, even when KVM was built with CONFIG_KVM_HYPERV=n, as KVM subtly relies on the "check" to clear the flag and thus avoid double-mapping the vmcs12 pages, e.g. if KVM manages to bail from VM-Enter without processing the request, and then emulates VMLAUNCH or VMRESUME. Fixes: b4f69df ("KVM: x86: Make Hyper-V emulation optional") Cc: stable@vger.kernel.org Reported-by: Yosry Ahmed Reviewed-by: Yosry Ahmed Link: https://patch.msgid.link/20260724004757.131420-2-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/kvm/vmx/nested.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=ae190f2439ca30067927077bf570d4c5edf07a0f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89931 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89931 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:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.7 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: 2 Paranoid ActionableScore: 3 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: MODERATE KPANIC detected for this report: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).