From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98463][MODERATE 7.0] sched_ext: Derive SCX_RQ_IN_WAKEUP from the core enqueue flags [ Upstream Date: Mon, 19 Oct 2026 05:49:04 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98463 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 6c401ae426e20e53a3398a8e79afd0964c0f5110 List-Id: CVE: CVE-2026-98463 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: sched_ext: Derive SCX_RQ_IN_WAKEUP from the core enqueue flags [ Upstream Commit: 6c401ae426e20e53a3398a8e79afd0964c0f5110 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c401ae426e20e53a3398a8e79afd0964c0f5110 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98463 Analysis date: Mon, 19 Oct 2026 05:49:04 -0400 ActionableScore: 4 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: A sched_ext flag propagation error can leave a deferred request linked after its scheduler per-CPU storage is freed, allowing the next scheduler to dereference stale kernel memory and potentially crash the host. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98463 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98463 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-2026-98463 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98463 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An incorrect wakeup state in sched_ext can leave a deferred local reenqueue action linked but unscheduled after a remote task activation. If the scheduler is disabled before the deferred action runs, the request can outlive the scheduler and retain a pointer into its freed per-CPU area. A later scheduler can dereference the stale request from run_deferred, creating a kernel use-after-free condition. Reliable triggering requires an active sched_ext scheduler, an IMMED insertion into a busy destination CPU, delayed deferred action processing, scheduler shutdown, and later execution of run_deferred, so AC:H is appropriate. For the CVSS the PR:L value in the paranoid score reflects environments where an untrusted local user can generate the required scheduling workload while a privileged service independently manages scheduler replacement or shutdown. The base assessment uses PR:H because direct control over loading or disabling a sched_ext scheduler is normally privileged. The issue is not network reachable. Impact is at least a local denial of service through a kernel crash and in the worst case may include confidentiality and integrity impact if the freed per-CPU allocation is reclaimed with attacker influenced data before the stale request is dereferenced. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 4.2 and ActionableScore 1 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE UAF HARDWARE LINUS KPANIC - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO ## 1. ActionableScore * Raw conservative score: 3 * Conservative score: 4 * Raw paranoid score: 3 * Paranoid score: 4 * Applied conservative REAL UAF FLOOR 4: 3 -> 4 * Applied paranoid REAL UAF FLOOR 4: 3 -> 4 * Final recommended bucket: **Borderline / manual review recommended**:: ## 2. Signal breakdown * +2 Real UAF. A deferred request remains linked after the owning sched_ext scheduler and its per-CPU storage are freed. `run_deferred()` later dereferences the stale request. * +1 Reliable kernel crash or strong DoS. Dereferencing freed per-CPU scheduler memory can produce a kernel fault. This crash is counted only once. * +0 Structured stale-object leverage. The request is active linked scheduler state, but attacker-controlled reclaim, replacement contents, callbacks, offsets, or pointers consumed after reuse are not established. * +0 Attacker-influenced lifetime manipulation. A workload may influence remote activation, but the evidence does not establish that the same below-admin attacker can also disable and replace the scheduler. * +0 Strong or weak LPE leverage. The UAF alone does not establish controlled reclaim, arbitrary read or write, callback control, or credential modification. * +0 Race penalty. This is primarily a state and ordering sequence. The patch does not establish a narrow, low-probability race requiring an uncontrollable timing window. * +0 Privilege penalty. Privileged scheduler management is plausible, but the complete attacker model is unresolved. No unsupported host-admin penalty is applied. * +0 Additional availability. The same potential kernel fault is not counted a second time. * +0 Confidentiality or integrity. No disclosure, directed write, or protected-state modification is demonstrated. The first lifetime-ending event is freeing the old scheduler per-CPU area. The exact linked deferred request survives and is later dereferenced, but no second `put`, `free`, or refcount mutation occurs. Therefore, the concrete repeated release/refcount signal and FLOOR 5 do not apply. B5-R, B3-PENDING, V33, V32, and B4-PENDING do not apply. There is no heap OOB write, shared-backing write, checksum metadata corruption, trust-boundary state corruption, or authorization decision bypass. ## 3. Reachability analysis The sequence requires an active sched_ext scheduler, remote activation carrying `ENQUEUE_WAKEUP`, an IMMED insertion into a busy destination CPU, a deferred request that remains pending, scheduler disablement, and later processing by the next scheduler. An ordinary task may contribute scheduling activity, but the supplied evidence does not prove that it can force the complete scheduler disable and replacement sequence. Conversely, the evidence does not prove that the attacker must personally possess host-administrator powers because a separate scheduler-management service could perform the lifecycle transition. The complete trigger is therefore compound or unresolved, so `HostAdminRequired=UNKNOWN`. sched_ext scheduler lifecycle management is host-global rather than an attacker-created user or network namespace operation. The complete trigger is not namespace-scoped, and no network-reachable path is established. No special hardware is required. ## 4. Primitive and severity interpretation The exact primitive is a use-after-free of an active deferred-action request pointing into freed scheduler per-CPU storage. It is an active structured lifetime object, but the stale use shown is a narrow teardown-to-next-scheduler dereference. This is CLASS_B because an actual post-lifetime dereference is established. It is not CLASS_A because controlled reclaim, attacker-shaped replacement data, useful field consumption, arbitrary kernel access, callback control, and privilege escalation are not demonstrated. The patch-supported consequence is kernel crash or DoS. Memory reuse could theoretically produce effects beyond an immediate fault, but the supplied call path does not establish meaningful exploitation leverage. Therefore, `ImportantCandidate=NO`, while manual review remains recommended because the defect is a real kernel UAF. `AutoDowngradeAllowed=YES` is appropriate for this constrained per-CPU teardown case unless additional source context shows controlled reuse or a below-admin complete trigger. ## 5. One-sentence report phrase A sched_ext flag propagation error can leave a deferred request linked after its scheduler per-CPU storage is freed, allowing the next scheduler to dereference stale kernel memory and potentially crash the host. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED The UAF is concrete, but the available evidence supports a constrained teardown-related crash path rather than an Important-grade exploitation primitive. ## 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: sched_ext: Derive SCX_RQ_IN_WAKEUP from the core enqueue flags [ Upstream Commit: 6c401ae426e20e53a3398a8e79afd0964c0f5110 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c401ae426e20e53a3398a8e79afd0964c0f5110 Changed files: kernel/sched/ext.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=6c401ae426e20e53a3398a8e79afd0964c0f5110 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98463 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98463 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:H/I:H/A:H The Best / paranoid CVSS score: 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: 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: YES 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).