From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64282][LOW] KVM: arm64: Don't leak PFN when kvm_translate_vncr() races MMU notifier Date: Sat, 25 Jul 2026 06:12:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64282 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: 0c93681aea0a1b8be14730a88abe77c840272e41 List-Id: CVE: CVE-2026-64282 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: KVM: arm64: Don't leak PFN when kvm_translate_vncr() races MMU notifier Commit: 0c93681aea0a1b8be14730a88abe77c840272e41 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c93681aea0a1b8be14730a88abe77c840272e41 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64282 Analysis date: Sat, 25 Jul 2026 06:12:12 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A race in KVM arm64 nested VNCR translation can leak a faulted PFN reference when an MMU notifier retry path returns early, allowing a local KVM user to cause possible host memory pressure or DoS under repeated race conditions. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64282 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64282 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-2026-64282 LOW 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-772;**CWE-400;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A PFN reference leak can occur in the KVM arm64 nested virtualization path when kvm_translate_vncr races with an MMU notifier. The function faults in a page and then returns EAGAIN on mmu_invalidate_retry, but the old error path did not drop the unused faulted page reference. A guest workload that can trigger VNCR_EL2 faults while host memory invalidation occurs may leak page references over repeated races, causing host memory pressure or denial of service. For the CVSS the PR:L is used because reliable triggering requires local ability to run or control a KVM VM on the host, for example access to /dev/kvm or a VM management context. The issue is not network reachable. Impact is resource exhaustion and denial of service rather than information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-64282 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 069a05e53549685d2b5e54ceb51db1fd04aa50d7 YES NO NO unknown MAYBE VIRT SIMPLEFIX RACE LEAK HARDWARE LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like** ## 2. Signal breakdown * Local low-privileged KVM trigger: +1 Triggering requires the ability to run or control a KVM VM, typically via `/dev/kvm` or a VM management context. This is not remote and not a normal unauthenticated interface. * Refcount / lifetime resource leak: +1 The bug leaks a reference on a faulted-in PFN when `kvm_translate_vncr()` races with an MMU notifier and returns `-EAGAIN` without releasing the page. * Availability impact realistic: +1 in paranoid scoring Repeated successful races could accumulate leaked page references and create host memory pressure or resource exhaustion. * Hard race / special timing required: -1 The leak requires a race with MMU notifier invalidation. * Rare / configuration-dependent path: -1 The affected path is KVM arm64 nested virtualization VNCR handling, not a broad default kernel path. * No generic memory corruption: +0 The patch shows a missing `kvm_release_faultin_page()` on an early error path. It does not show UAF, stale rmap traversal, OOB write, type confusion, arbitrary write, or page-cache corruption. * No LPE signal: +0 There is no evidence of attacker-controlled reclaim, object replacement, callback control, stale pointer reuse, or write primitive. Call-site confidence: high. The relevant call path and missing release are visible in the patch. ## 3. Reachability analysis The issue can be triggered by a local actor able to run or influence a KVM arm64 nested virtualization workload that reaches `kvm_translate_vncr()`. In typical deployments this requires access to `/dev/kvm`, membership in a virtualization-related group, or control over a VM through a management stack. It is not network reachable by itself. Containers and namespaces do not normally make this reachable unless KVM device access is explicitly delegated. Realistic exploitation requires repeatedly hitting a race with MMU notifier invalidation, so the practical impact is resource leakage rather than immediate compromise. ## 4. Severity interpretation This behaves like an ordinary Moderate / Low-like resource leak. The theoretical worst case is host memory pressure or denial of service after repeated successful races. The patch does not support treating it as memory corruption or privilege escalation. It is not covered by the KVM rmap stale-pointer rule because the fix does not involve SPTE overwrite, stale reverse mappings, page table traversal after free, or wrong-object freeing. ## 5. One-sentence report phrase A race in KVM arm64 nested VNCR translation can leak a faulted PFN reference when an MMU notifier retry path returns early, allowing a local KVM user to cause possible host memory pressure or DoS under repeated race conditions. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: this is a local KVM PFN reference leak with hard race requirements, no demonstrated memory corruption, no security-boundary bypass, and no plausible privilege escalation primitive in the provided patch context. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: arm64: Don't leak PFN when kvm_translate_vncr() races MMU notifier Commit: 0c93681aea0a1b8be14730a88abe77c840272e41 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c93681aea0a1b8be14730a88abe77c840272e41 Commit description: In the case that kvm_translate_vncr() races with an MMU notifier the early return does not release a reference on the faulted in PFN. Add the necessary call to kvm_release_faultin_page() for the unused PFN. Cc: stable@vger.kernel.org Fixes: 069a05e ("KVM: arm64: nv: Handle VNCR_EL2-triggered faults") Reported-by: Sashiko (local):gemini-3.1-pro Signed-off-by: Oliver Upton Link: https://patch.msgid.link/20260602235450.103057-2-oupton@kernel.org Signed-off-by: Marc Zyngier Signed-off-by: Greg Kroah-Hartman Changed files: arch/arm64/kvm/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=0c93681aea0a1b8be14730a88abe77c840272e41 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64282 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64282 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: 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).