From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72277][MODERATE REGULAR] KVM: arm64: nv: Inject SEA if guest VNCR isn't normal memory commit 4bd7dbe0b2243e6aa735cae4d5e1ff988b30b2a6 upstream. Date: Sat, 15 Aug 2026 17:01:00 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72277 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: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: d5436e18e4fc2886ac306304d884ea3b92e1edbf List-Id: CVE: CVE-2026-72277 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: KVM: arm64: nv: Inject SEA if guest VNCR isn't normal memory commit 4bd7dbe0b2243e6aa735cae4d5e1ff988b30b2a6 upstream. Commit: d5436e18e4fc2886ac306304d884ea3b92e1edbf Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5436e18e4fc2886ac306304d884ea3b92e1edbf Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72277 Analysis date: Sat, 15 Aug 2026 17:01:00 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline manual-review / Actionable Moderate candidate Manual review required: YES Summary: KVM arm64 nested virtualization may map a guest VNCR using cacheable attributes for a non-normal-memory PFN, allowing a local KVM-capable actor to trigger a host SError and cause a host kernel crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72277 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72277 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-2026-72277 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H';CWE-755;CWE-703;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'KVM arm64 nested virtualization could create an L1 VNCR mapping with cacheable memory attributes even when the backing PFN is not normal memory. If the endpoint does not support those cacheable attributes, a writeback may raise a host SError and can crash the host kernel. For the CVSS the PR:L is used for the paranoid score because a local actor with access to KVM or a tenant controlled VMM context may be able to provide the relevant nested VM state and backing mapping without full host administrator privileges. The issue is not directly network reachable and requires local virtualization control rather than packet traffic. Impact is denial of service via host crash. There is no concrete UAF, OOB write, arbitrary write, or information leak primitive visible from this patch, so confidentiality and integrity are not raised.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual-review / Actionable Moderate candidate (with actual score 4) SKIP CVE-2026-72277 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 2a359e072596fcb2e9e85017a865e3618a2fe5b5 YES NO NO unknown MAYBE VIRT SIMPLEFIX HARDWARE LINUS INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline manual-review / Actionable Moderate candidate**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1 A local actor with access to `/dev/kvm`, or a tenant-controlled VMM context, may be able to influence nested guest VNCR state and backing mappings. This is not remote network reachable. * Reliable kernel crash / strong DoS: +1 The commit explicitly describes a host SError on writeback when cacheable attributes are used for a non-normal-memory PFN. This can crash the host kernel. * Cross-boundary isolation impact: +1 The failure crosses the guest or VMM to host availability boundary. Even though the demonstrated impact is DoS only, crashing the host from a guest-controlled virtualization path is operationally significant. * Rare or configuration-dependent path: -1 This depends on arm64 KVM nested virtualization and a non-normal-memory PFN or PFNMAP-like backing condition. It is not a broad default kernel path. Paranoid additional interpretation: * Availability impact realistic: +1 If reachable in a deployed nested virtualization setup, the impact is host-wide and affects all workloads on the host, not only the triggering VM. No awarded signals: * No generic strong memory corruption: +0 The patch does not show UAF, double free, OOB write, arbitrary write, refcount takeover, or type confusion. * No privilege escalation plausible: +0 The supported primitive is host crash via SError, not LPE or guest-to-host code execution. * No confidentiality or integrity impact: +0 The patch provides no evidence of information disclosure, attacker-controlled writes, page-cache corruption, or ownership bypass. ## 3. Reachability analysis The bug is reachable through KVM arm64 nested virtualization when KVM constructs an L1 VNCR mapping backed by a PFN that is not normal memory. A local user or service with KVM access may be able to trigger it if the environment allows nested virtualization and suitable backing mappings. In typical deployments, `/dev/kvm` access may be delegated to non-root users through a `kvm` group, so PR:L is a defensible paranoid interpretation. This is not directly network reachable and packet traffic is not involved. Containers only matter if KVM device access is passed through into the container. Call-site confidence: medium. The patch shows the failing helper path and concrete failure mode, but not the full VMM-controlled setup path. ## 4. Severity interpretation This behaves more like a borderline or actionable Moderate virtualization-boundary DoS than an Important memory-corruption issue. The theoretical concern is guest or VMM influence over a host crash condition, but the patch does not support a stronger primitive such as UAF, arbitrary write, or privilege escalation. Manual review is justified because KVM guest-to-host availability bugs can be deployment sensitive, especially when `/dev/kvm` is available to tenant workloads. ## 5. One-sentence report phrase KVM arm64 nested virtualization may map a guest VNCR using cacheable attributes for a non-normal-memory PFN, allowing a local KVM-capable actor to trigger a host SError and cause a host kernel crash. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This should not be auto-closed because it is a KVM virtualization-boundary issue with a plausible guest or VMM controlled host crash path, even though the patch currently supports DoS only and not memory corruption or privilege escalation. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: arm64: nv: Inject SEA if guest VNCR isn't normal memory commit 4bd7dbe0b2243e6aa735cae4d5e1ff988b30b2a6 upstream. Commit: d5436e18e4fc2886ac306304d884ea3b92e1edbf Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5436e18e4fc2886ac306304d884ea3b92e1edbf Commit description: When constructing an L1 VNCR mapping, KVM unconditionally uses cacheable memory attributes, even if the underlying PFN isn't memory. This gets particularly hairy if the endpoint doesn't support cacheable memory attributes, potentially throwing an SError on writeback... While KVM does permit cacheable memory attributes on certain PFNMAP VMAs, kvm_translate_vncr() isn't currently grabbing the VMA. So do the simpler thing for now and just reject everything that isn't memory. Cc: stable@vger.kernel.org Fixes: 2a359e072596 ("KVM: arm64: nv: Handle mapping of VNCR_EL2 at EL2") Signed-off-by: Oliver Upton Link: https://patch.msgid.link/20260618234207.1063941-5-oupton@kernel.org Signed-off-by: Marc Zyngier Signed-off-by: Greg Kroah-Hartman Diffstat -rw-r--r-- arch/arm64/kvm/nested.c 11 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=d5436e18e4fc2886ac306304d884ea3b92e1edbf ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72277 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72277 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:C/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/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: 3 Paranoid ActionableScore: 4 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).