From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98877][MODERATE REGULAR] irqchip/gic-v4: Don't advertise VLPIs if no ITS is probed [ Upstream Date: Mon, 26 Oct 2026 21:19:59 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98877 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 3e4cae9f1472ba3c9fe87edee24074618b51f537 List-Id: CVE: CVE-2026-98877 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: irqchip/gic-v4: Don't advertise VLPIs if no ITS is probed [ Upstream Commit: 3e4cae9f1472ba3c9fe87edee24074618b51f537 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e4cae9f1472ba3c9fe87edee24074618b51f537 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98877 Analysis date: Mon, 26 Oct 2026 21:19:59 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A local KVM user can panic a specially misconfigured ARM GICv4 host because vLPI support remains advertised despite the absence of an ITS. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98877 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98877 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98877 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98877 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-670;CWE-665;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A GICv4 initialization logic error can leave vLPI support advertised when no ITS was probed. With kvm-arm.vgic_v4_enable enabled, a local KVM user can reach GICv4 setup with a NULL gic_domain and cause a host kernel panic. For the CVSS the PR:L value reflects the need for local access to KVM or an equivalent virtualization service after the vulnerable host configuration already exists. The issue is not directly network reachable and the demonstrated primitive is a NULL pointer dereference with availability impact only. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 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. 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_CIANNH and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 4.2 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE OOB DANGER NULLPTR HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 2. * Conservative score: 2; no floor or cap applied. * Raw paranoid score: 2. * Paranoid score: 2; no additional technically supported primitive. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Local below-host-admin trigger: supplied evidence identifies a local KVM user with access to the virtualization interface after host configuration. * +1 Reliable kernel crash: enabling GICv4 setup without an ITS leaves `gic_domain` NULL, producing the documented host-kernel NULL dereference. * No configuration penalty: the mismatched GICv4 setting is unusual and requires prior host configuration, but the vulnerable path is straightforward once that configuration exists. * No UAF, OOB write, attacker-controlled corruption, authorization bypass, confidentiality impact, or integrity impact is shown. * No extra availability point: it would duplicate the same host panic. * B5-R does not apply: there is no retry-accumulated heap write or later consumption of corrupted structured state. * B3/B4 pending profiles do not apply: neither shared-backing modification nor a DENY-to-ALLOW authorization change exists. 3. Reachability analysis A local user with usable KVM access can create the triggering VM under the pre-existing vulnerable host configuration. Host UID 0 or host-administrator powers are not shown as necessary for the runtime trigger, although a host administrator likely established the `kvm-arm.vgic_v4_enable=1` configuration. No guest-only trigger is demonstrated: this is a local VMM/KVM-user path. It requires ARM GICv4 hardware or emulation, no probed ITS, and the inconsistent enablement setting. No race or network reachability is involved. 4. Primitive and severity reading The exact primitive is a deterministic NULL-pointer dereference during GICv4 IRQ-domain setup. This is CLASS_C crash/DoS behavior, not memory corruption or stale-object use. The fix clears `has_vlpis` when no ITS exists, preventing unsupported vLPI capability propagation into KVM. No useful effect remains after excluding the crash, so Important candidacy is unsupported and automatic Moderate handling remains permissible. 5. One-sentence report phrase A local KVM user can panic a specially misconfigured ARM GICv4 host because vLPI support remains advertised despite the absence of an ITS. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm product exposure to the inconsistent boot configuration and whether untrusted users receive KVM device access. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: irqchip/gic-v4: Don't advertise VLPIs if no ITS is probed [ Upstream Commit: 3e4cae9f1472ba3c9fe87edee24074618b51f537 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e4cae9f1472ba3c9fe87edee24074618b51f537 Changed files: drivers/irqchip/irq-gic-v3-its.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=3e4cae9f1472ba3c9fe87edee24074618b51f537 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98877 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98877 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:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: unknown 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: 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).