From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99251][LOW] Drivers: hv: Avoid infinite retry loop in init_vp_index() [ Upstream Date: Tue, 03 Nov 2026 23:01:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99251 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: b3993f6dc106ff416c7a613c631e1e0af451aed7 List-Id: CVE: CVE-2026-99251 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: Drivers: hv: Avoid infinite retry loop in init_vp_index() [ Upstream Commit: b3993f6dc106ff416c7a613c631e1e0af451aed7 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3993f6dc106ff416c7a613c631e1e0af451aed7 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99251 Analysis date: Tue, 03 Nov 2026 23:01:26 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A host-admin-controlled Hyper-V guest CPU-isolation topology can cause VMBus channel initialization to retry indefinitely, with no demonstrated memory corruption or authorization impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99251 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99251 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-2026-99251 LOW https://www.kernelcve.org/list/?q=CVE-2026-99251 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both 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:N/I:N/A:H';*CWE-835;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A logic error in Hyper V VMBus CPU selection can make init_vp_index retry indefinitely when the selected NUMA node has CPUs but none belong to the HK_TYPE_MANAGED_IRQ housekeeping mask. The condition requires a Hyper V guest with a performance critical channel and a specific CPU isolation and NUMA arrangement. For the CVSS the PR:H value reflects that reliable triggering normally requires administrative control over boot time CPU isolation or equivalent system configuration. The impact is availability loss through a stuck channel initialization path and CPU spinning. There is no supported memory corruption or confidentiality or integrity primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. 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 SIMPLEFIX LEAK HARDWARE LINUS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=NONE 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 base score: -2. * Conservative score: 0, normalized at the lower bound. * Raw paranoid score: -2. * Paranoid score: 0, normalized at the lower bound. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable DoS: the uncorrected retry loop can spin indefinitely and prevent completion of VMBus channel initialization. * -2 Proven effective host-administrator prerequisite: reliable triggering requires control over system-wide CPU isolation/housekeeping configuration. * -1 Rare and difficult configuration: the affected Hyper-V guest must have a performance-critical channel plus a NUMA node containing CPUs but no eligible online managed-IRQ housekeeping CPU. * No memory corruption, OOB access, UAF, corrupted-state consumption, confidentiality impact, integrity impact, or authorization bypass is shown. * B5-R does not apply: retries do not accumulate an index or offset into a heap OOB write, and no later corrupted descriptor is consumed. * No extra availability point: the stuck initialization loop is the sole demonstrated effect. 3. Reachability analysis The vulnerable path runs during Hyper-V VMBus channel setup, but the triggering topology depends on global NUMA and housekeeping/CPU-isolation state. Supplied evidence supports effective administrative control over that setup, not an ordinary user or namespace-scoped capability. Numeric host UID 0 specifically is not established. No separate remote, guest-user, delegated-interface, or namespace trigger is shown. This is a deterministic logic condition once the unusual configuration exists, rather than a timing race. 4. Primitive and severity reading The exact defect is failure to skip a NUMA node having no housekeeping CPU, causing retry without progress. It is a pure infinite-loop/resource-consumption condition, classified NONE rather than a corruption primitive. The fix restores progress by selecting only intersecting nodes and checking for online housekeeping CPUs. ImportantCandidate is NO and auto-downgrade is allowed because there is no non-availability primitive or unresolved trust-boundary effect. 5. One-sentence report phrase A host-admin-controlled Hyper-V guest CPU-isolation topology can cause VMBus channel initialization to retry indefinitely, with no demonstrated memory corruption or authorization impact. 6. Manual review advice NO MANUAL CHECK NEEDED The patch and supplied context establish only a configuration-dependent availability failure. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: Drivers: hv: Avoid infinite retry loop in init_vp_index() [ Upstream Commit: b3993f6dc106ff416c7a613c631e1e0af451aed7 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3993f6dc106ff416c7a613c631e1e0af451aed7 Changed files: drivers/hv/channel_mgmt.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=b3993f6dc106ff416c7a613c631e1e0af451aed7 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99251 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99251 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: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: 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).