From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98390][LOW] x86/amd_node: Avoid divide by zero on virtualized systems Date: Wed, 14 Oct 2026 22:57:23 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98390 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: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 9273a90465d58b82aca4bea71451ef6bee084928 List-Id: CVE: CVE-2026-98390 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: x86/amd_node: Avoid divide by zero on virtualized systems Commit: 9273a90465d58b82aca4bea71451ef6bee084928 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9273a90465d58b82aca4bea71451ef6bee084928 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98390 Analysis date: Wed, 14 Oct 2026 22:57:23 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98390 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98390 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-2026-98390 LOW https://www.kernelcve.org/list/?q=CVE-2026-98390 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-369;CWE-682;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.4';DESCR 'A divide by zero can occur during x86 AMD node initialization because num_roots may be smaller than num_nodes on a virtualized system, producing roots_per_node equal to zero. A later modulo operation using roots_per_node can raise a fatal exception and prevent the affected kernel from completing initialization. Xen PVH dom0 is a confirmed configuration, although other virtualized platforms with a similar topology may also be affected. For the CVSS the PR:H reflects that reliable triggering requires control over the virtual hardware or NUMA topology, which normally belongs to a hypervisor administrator rather than an ordinary user inside the affected system. The issue is not network reachable. Impact is denial of service through a boot time kernel crash, with no supported memory corruption, information disclosure, or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.4 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3. The independent weaker Aegis shadow evaluated CVSS 4.5 and ActionableScore 0 with primitive class CLASS_C and manual review NO. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE DANGER UAF KERNEL_PANIC_PLUS_UAF HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: -1 * Conservative score: 0 * Raw paranoid score: -1 * Paranoid score: 0 * Applied score lower bound: -1 -> 0 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel crash. `roots_per_node` becomes zero when `num_roots < num_nodes`, and the subsequent modulo operation causes a divide-by-zero exception during kernel initialization. * -2 Proven host-admin-equivalent prerequisite. Deliberately controlling the virtual hardware or NUMA topology presented to Xen PVH dom0 requires control of the hypervisor or equivalent host configuration. * No additional rare-configuration penalty was applied because the Xen topology prerequisite overlaps substantially with the host-administrator restriction. * No memory-corruption signal. The primitive is an arithmetic exception, not an OOB access, UAF, overwrite, or stale-object operation. * No extra Availability point. The boot failure and kernel crash are the same consequence. * No confidentiality, integrity, authorization, ownership, or security-boundary signal. * B5-R does not apply because there is no heap OOB write, retry accumulation, or later consumption of corrupted state. * B3-PENDING and B4-PENDING do not apply because there is no shared-backing write or authorization decision. 3. Reachability analysis The confirmed affected configuration is Xen PVH dom0 with `num_nodes` equal to 2 and `num_roots` equal to 1. The failure occurs in `amd_smn_init()` during kernel initialization and is deterministic once that topology is present. No ordinary local-user, namespace-capability, device ioctl, or network trigger is established. The complete operation is not namespace-scoped. An intentional attacker would need effective control over the hypervisor or host topology configuration. The evidence does not establish that numeric host UID 0 specifically is mandatory, because equivalent authority could be exercised through a privileged virtualization management service. There is no race or retry requirement. Other virtualization environments might be affected, but no additional attacker-accessible path is established. 4. Primitive and severity interpretation The exact primitive is integer division followed by modulo using a zero divisor. It causes a synchronous exception and boot-time denial of service. This is `CLASS_C` crash behavior. It is neither active structured-object corruption nor fixed stale storage, and no repeated release or refcount operation exists. There is no leverage beyond preventing initialization of the affected kernel. `ImportantCandidate=NO` because no memory corruption, authorization bypass, cross-boundary effect, or below-host-admin trigger is supported. `AutoDowngradeAllowed=YES` because the demonstrated result is a configuration-dependent crash with no unresolved exploitation primitive. The likely operational severity is Low-like to ordinary Moderate, despite CVSS availability scoring, because the party able to intentionally construct the triggering topology already controls the affected host virtualization environment. 5. One-sentence report phrase A virtualized AMD system can calculate roots_per_node as zero and crash during kernel initialization when the value is later used as a modulo divisor, but intentional triggering requires control over the host virtual topology and exposes no memory corruption or privilege escalation primitive. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a deterministic divide-by-zero DoS with a host-administrator-controlled prerequisite and no unresolved corruption or security-boundary primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: x86/amd_node: Avoid divide by zero on virtualized systems Commit: 9273a90465d58b82aca4bea71451ef6bee084928 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9273a90465d58b82aca4bea71451ef6bee084928 Commit description: On a virtualized system, the number of nodes does not have a relationship to the number of roots. A Xen PVH dom0 can calculate roots_per_node as 0, which crashes with a divide by zero in: if (count++ % roots_per_node) because the underlying topology code on Xen ends up making num_nodes 2 and num_roots 1 and the integer division result is 0. The issue is seen with Xen, but it could affect other systems. Set roots_per_node to 1 in this case. Print a firmware bug when this is performed for non-virtualized systems. [ bp: Massage commit message. ] Fixes: 0a4b61d ("x86/amd_node: Fix AMD root device caching") Suggested-by: Borislav Petkov Signed-off-by: Jason Andryuk Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Yazen Ghannam Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260825214805.39148-2-jason.andryuk@amd.com Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/kernel/amd_node.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=9273a90465d58b82aca4bea71451ef6bee084928 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98390 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98390 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:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.4 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: 0 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).