[CVE-2026-98814][MODERATE 7.0] nvme: fix command effects log lifetime for multipath heads [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98814
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nvme: fix command effects log lifetime for multipath heads [ Upstream
Commit: 351d1c47e45b2b35780d0548b1012d7242ba298d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=351d1c47e45b2b35780d0548b1012d7242ba298d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98814
Analysis date: Fri, 23 Oct 2026 20:45:27 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
An NVMe multipath namespace head can retain a controller-owned command-effects log after it is freed, causing a local passthrough ioctl to read stale slab data in `nvme_command_effects()` and potentially crash the kernel or influence command validation.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98814 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98814

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98814	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98814 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 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:L/I:L/A:H';*CWE-416;*CWE-664;CWE-825;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A slab use-after-free can occur because an NVMe multipath namespace head may retain a command effects log pointer owned by the controller path that originally created the head. After that controller path is removed, a later I/O passthrough ioctl through the surviving namespace head can reach nvme_command_effects and read four bytes from freed slab memory. The demonstrated primitive is a stale read rather than an arbitrary write. It can cause a kernel warning or crash and reclaimed contents may also influence the command authorization decision made by nvme_cmd_allowed. For the CVSS the PR:L value is used because a local process must be able to open the NVMe namespace head character device and issue a passthrough ioctl. AC:H reflects the required multipath lifetime sequence involving removal of the originating controller path followed by access through the surviving namespace head. The issue is not directly network reachable even when the underlying NVMe path uses a network fabric. Impact is at least a local denial of service via a kernel fault. In the paranoid interpretation limited confidentiality or integrity impact remains plausible because reused slab contents can affect command effects validation, but the available code does not establish an arbitrary write or reliable privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.8 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. 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 2.5 and ActionableScore 4 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 Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	READ LOCK DANGER INIT NVME UAF LOG HARDWARE LINUS KPANIC 	-	-	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative floor: 3 -> 5 under REAL UAF FLOOR 5 because the active stale object is consumed by security-relevant command validation rather than only by cleanup code.
* Applied paranoid floor: 4 -> 5 for the same reason.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Real UAF: a multipath namespace head retains `ctrl->effects` after the controller-owned command-effects log is freed.
* +1 Weak exploitation concern: the stale four-byte value is consumed by `nvme_cmd_allowed()`, so reclaimed contents can affect command-effects validation rather than merely causing an immediate cleanup fault.
* Paranoid +1 Reliable kernel crash concern: KASAN confirms a slab UAF, and dereferencing reclaimed storage can realistically cause a kernel fault. This is not counted again as a separate availability impact.
* No privilege penalty: host-admin-equivalent privilege for the complete sequence is not established.
* No race penalty: the demonstrated sequence is controller-path removal followed by an ioctl, not a proven narrow timing race.
* No structured stale-object leverage point: attacker control of reclaim, replacement contents, or slab placement is not established.
* No strong exploitation-leverage point: arbitrary write, controlled reclaim, callback control, disclosure, and privilege escalation are not demonstrated.
* No confidentiality or integrity point: influence over `nvme_cmd_allowed()` is unresolved and does not establish access to a protected resource.
* No repeated-release point: there is no second `put`, `free`, or refcount mutation through the stale pointer.
* B5-R does not apply because there is no retry-accumulated OOB write.
* B3-PENDING does not apply because there is no shared-backing write.
* B4-PENDING does not apply because the patch does not establish omission of a mandatory authorization guard or a concrete DENY-to-ALLOW path.

3. Reachability analysis

The demonstrated trigger requires an NVMe multipath namespace head, removal of the controller path that originally supplied the command-effects log, and a later I/O passthrough ioctl through the surviving namespace head.

The ioctl caller must be able to open the relevant NVMe character device and issue passthrough commands. The supplied evidence does not establish whether this requires host root, a delegated storage-management service, or a below-host-admin user under the affected deployment. Therefore `HostAdminRequired` and `RequiresHostUID0` remain `UNKNOWN`.

No user-namespace or namespace-scoped capability path is established. Network fabrics may underlie the controller path, but the vulnerable operation is a local ioctl and is not directly triggered by an ordinary network packet. No timing race is required by the documented reproducer sequence.

4. Primitive and severity interpretation

The exact primitive is a four-byte slab use-after-free read from a freed `nvme_effects_log`. It is an active structured-object lifetime bug because the stale value is used during live passthrough-command validation after controller teardown. It is not limited to a destructor or cleanup helper.

This is `CLASS_B`, not `CLASS_A`. The code establishes neither an OOB write nor controlled post-free replacement. It also does not establish a concrete authorization bypass because no specific stale value is shown to convert a mandatory denial into permission for a protected operation.

The demonstrated consequence is KASAN detection of a real UAF. A warning or kernel crash is plausible. The unresolved consequence is that reused slab contents may alter the command-effects result consumed by `nvme_cmd_allowed()`. That unresolved active-use behavior justifies mandatory review, but it does not prove arbitrary command authorization, storage corruption, information disclosure, or privilege escalation.

`ImportantCandidate=YES` preserves review of this active structured UAF and its command-validation sink. `AutoDowngradeAllowed=NO` is appropriate because automatically treating it as an ordinary crash-only UAF would discard the unresolved effect of stale data on a privileged downstream consumer.

5. One-sentence report phrase

An NVMe multipath namespace head can retain a controller-owned command-effects log after it is freed, causing a local passthrough ioctl to read stale slab data in `nvme_command_effects()` and potentially crash the kernel or influence command validation.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The UAF is confirmed and the stale data is consumed by `nvme_cmd_allowed()`, while device permissions, reclaim influence, and the resulting command-policy impact remain unresolved.

7. Call-site confidence

Call-site confidence: high

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: nvme: fix command effects log lifetime for multipath heads [ Upstream
Commit: 351d1c47e45b2b35780d0548b1012d7242ba298d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=351d1c47e45b2b35780d0548b1012d7242ba298d

Changed files:
  drivers/nvme/host/core.c
  drivers/nvme/host/nvme.h

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=351d1c47e45b2b35780d0548b1012d7242ba298d

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98814 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98814

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 5

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).