From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72279][MODERATE 7.0] KVM: arm64: nv: Respect read-only PFN when mapping L1 VNCR Date: Sat, 15 Aug 2026 05:00:38 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72279 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 5c50db5bcbb9073cb2fd97be51b962de92f429e9 List-Id: CVE: CVE-2026-72279 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: KVM: arm64: nv: Respect read-only PFN when mapping L1 VNCR Commit: 5c50db5bcbb9073cb2fd97be51b962de92f429e9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c50db5bcbb9073cb2fd97be51b962de92f429e9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72279 Analysis date: Sat, 15 Aug 2026 05:00:38 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: KVM arm64 nested virtualization could map an L1 VNCR backing PFN with writable host permissions despite the PFN being read-only, creating a local KVM memory-policy bypass risk and a page leak that warrants manual review. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72279 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72279 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 7.0 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-2026-72279 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H';CWE-284;CWE-732;*CWE-772;*CWE-401;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '6.5';DESCR 'KVM arm64 nested virtualization could map the L1 VNCR with writable host permissions even when the backing PFN is read-only, for example from a KVM_MEM_READONLY memslot. This can violate the expected read-only memory policy for the VNCR backing page and may also expose a page reference leak on the read-only fault path. For the CVSS the PR:L is used because an attacker needs local access to KVM ioctls or a VM process able to configure and run the affected nested virtualization path, but full host administrator privileges are not necessarily required in common /dev/kvm group deployments. The issue is not network reachable and is triggered through local KVM control and guest execution rather than packet traffic. Impact is at least a local denial of service or policy bypass, and in the paranoid interpretation may allow limited confidentiality impact and high integrity impact due to writable mapping of a read-only PFN.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) SKIP CVE-2026-72279 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 2a359e072596fcb2e9e85017a865e3618a2fe5b5 YES NO NO unknown MAYBE VIRT LEAK HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 Local access to `/dev/kvm` or a VM process with KVM access can plausibly reach this path. Full host root is not necessarily required in common KVM group deployments. * Weak or indirect corruption candidate: +1 The bug can create a writable host stage-1 mapping for a backing PFN that should be read-only. This is not an arbitrary write primitive, but it is a permission-sensitive memory mapping error. * Cross-boundary isolation or policy bypass: +1 `KVM_MEM_READONLY` or read-only PFN state is an intended memory protection boundary. Ignoring backing PFN writability can violate that policy. * Privileged kernel/device-management memory permission path: +1 The affected code is in KVM arm64 nested virtualization and controls host fixmap permissions for VNCR backing memory. This is a high-value MMU/page-permission path. * Availability impact realistic: +1 The commit explicitly mentions a page leak on the read-only PFN path. Repeated triggering can plausibly cause resource exhaustion. Subtractors: * Rare AND difficult-to-reach subsystem/configuration: -1 The issue requires arm64 KVM nested virtualization with VNCR handling and read-only PFN or RO memslot conditions, which is narrower than ordinary KVM execution. Paranoid-only elevation: * Integrity impact plausible: +1 The paranoid score treats writable mapping of a read-only PFN as a meaningful integrity concern, although the patch does not show arbitrary host memory write, UAF reclaim, callback control, or a demonstrated LPE chain. ## 3. Reachability analysis The bug is locally reachable through KVM arm64 nested virtualization paths. A realistic attacker would need the ability to run or control a VM using the affected nested virtualization feature and arrange a read-only PFN or `KVM_MEM_READONLY` backing condition. This is not network reachable. Privileges depend on deployment. On systems where `/dev/kvm` is available to non-root users in the `kvm` group, PR is closer to local low privilege. If KVM access is restricted to root or trusted virtualization services, practical reachability is much lower. Containers usually do not expose `/dev/kvm` by default, but VM service accounts or reduced-capability users may still be relevant. Call-site confidence: high. The patch includes the translation path, permission fault handling, page release behavior, dirty marking, and final fixmap permission selection. ## 4. Severity interpretation This is stronger than an ordinary low-risk resource leak because the main issue is a KVM MMU permission mismatch: guest stage-1 permissions could cause a host mapping to become writable even when the backing PFN is read-only. However, the patch does not demonstrate a strong memory corruption primitive such as UAF reclaim, arbitrary write, type confusion, or controlled overwrite of host kernel objects. Realistically, this behaves like an actionable Moderate KVM memory-permission bug with a page leak. Paranoid handling is justified because KVM memory permission mistakes can become security-boundary issues, but the evidence is not strong enough to classify it as a clear Important vulnerability without manual review. ## 5. One-sentence report phrase KVM arm64 nested virtualization could map an L1 VNCR backing PFN with writable host permissions despite the PFN being read-only, creating a local KVM memory-policy bypass risk and a page leak that warrants manual review. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the bug affects KVM arm64 nested virtualization MMU permissions and read-only PFN enforcement. The exploitability is configuration-dependent, but the affected primitive is security-sensitive enough that it should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: arm64: nv: Respect read-only PFN when mapping L1 VNCR Commit: 5c50db5bcbb9073cb2fd97be51b962de92f429e9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c50db5bcbb9073cb2fd97be51b962de92f429e9 Commit description: KVM currently maps the L1 VNCR into the host stage-1 by relying entirely on the permissions of the guest stage-1. At the same time, it is entirely possible that the backing PFN is read-only (e.g. RO memslot), meaning that the L1 VNCR should use at most a read-only mapping. Cache the writability of the PFN in the VNCR TLB and use it to constrain the resulting fixmap permissions. Promote VNCR permission faults to an SEA in the case where the guest attempts to write to a read-only endpoint. Conveniently, this also plugs a page leak found by Sashiko [*] resulting from the early return for a read-only PFN. Cc: stable@vger.kernel.org Fixes: 2a359e0 ("KVM: arm64: nv: Handle mapping of VNCR_EL2 at EL2") Link: https://lore.kernel.org/kvm/20260608082603.16AEC1F00893@smtp.kernel.org/ Signed-off-by: Oliver Upton Link: https://patch.msgid.link/20260618234207.1063941-2-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=5c50db5bcbb9073cb2fd97be51b962de92f429e9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72279 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72279 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:L/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H The Best / paranoid CVSS score: 6.5 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: 4 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: MODERATE KPANIC detected for this report: NO Published priority for this report (same as in Subject): MODERATE 7.0 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).