[CVE-2026-97989][LOW] vduse: validate virtqueue alignment [ Upstream

[CVE-2026-97989][LOW] vduse: validate virtqueue alignment [ Upstream

[AL-KERNEL]

CVE: CVE-2026-97989
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: vduse: validate virtqueue alignment [ Upstream
Commit: c3c3b0839a1197530cc18f535062fc84dbdfc885
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3c3b0839a1197530cc18f535062fc84dbdfc885
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97989
Analysis date: Fri, 25 Sep 2026 14:00:43 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An invalid VDUSE virtqueue alignment value can cause virtio split-ring initialization to leave the used-ring pointer NULL, allowing activation of the resulting virtio-net device to trigger a local kernel crash or denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-97989 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97989

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-2026-97989	LOW	https://www.kernelcve.org/list/?q=CVE-2026-97989 CHECK WITH IMPACT FROM ORIG NN LOW	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-20;CWE-1284;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'An invalid vq_align value in a VDUSE device configuration can reach the virtio split ring helpers without validation. A zero alignment value causes vring initialization to leave the used ring pointer NULL and opening the created virtio net device can dereference that pointer in virtqueue_kick_prepare_split, causing a kernel crash or denial of service. For the CVSS the PR:L in the paranoid score reflects deployments where VDUSE management is delegated to a service account, container root, or another user with limited administrative capabilities. Typical systems require CAP_SYS_ADMIN or equivalent administrative access to create and configure a VDUSE device. The issue is not network reachable. No confidentiality or integrity impact is supported because the patch demonstrates a NULL pointer dereference and not a memory corruption primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	READ KASAN OOB NULLPTR HARDWARE LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

The score is driven only by the demonstrated kernel crash or DoS consequence. No floor or cap changed the result.

## 2. Signal breakdown

* **+1 Reliable kernel crash or strong DoS.** A VDUSE device configured with `vq_align=0` can leave the virtqueue used-ring pointer NULL. Opening the resulting virtio-net device reaches `virtqueue_kick_prepare_split()` and dereferences that NULL pointer. The supplied KASAN trace directly supports this consequence.

Important non-awarded signals:

* **No UAF signal.** No object is freed, retained after lifetime end, reused, or accessed post-free.
* **No OOB read or write primitive.** The fault is a NULL-pointer read resulting from invalid ring initialization.
* **No arbitrary or directed kernel write.** The patch only demonstrates malformed alignment reaching virtio ring setup.
* **No controlled reclaim or object replacement.** No allocator reuse or replacement object is involved.
* **No confidentiality or integrity signal.** The supplied trace establishes a kernel NULL dereference, not disclosure, modification of protected data, or policy bypass.
* **No remote reachability signal.** The malformed `vq_align` value is supplied through VDUSE device configuration, not through ordinary network traffic.
* **No local-unprivileged-trigger signal.** The supplied patch does not establish that an ordinary user can create and configure a VDUSE device.
* **No host-admin penalty applied.** The supplied material does not show the exact capability check and user-namespace scope for the complete VDUSE create, configure, and activate sequence. Therefore `HostAdminRequired` is `UNKNOWN`, not `YES`.
* **No delegated-privilege interpretation applied.** The earlier hint that a service account or container root might have access is deployment speculation, not evidence that the full vulnerable sequence is available below host administration.
* **No additional Availability point.** The observed kernel crash is already counted by the single `+1 Reliable kernel crash or strong DoS` signal.

## 3. Reachability analysis

The immediate trigger is a locally created VDUSE device with an invalid virtqueue alignment value of zero. The attacker must be able to create or configure that VDUSE device and then cause a virtio-net interface backed by it to be opened.

VDUSE is a userspace vDPA device-management interface. In typical deployments its control operations are privileged and access to the VDUSE device node is restricted. However, the supplied patch does not include the relevant ioctl call sites, device-node permissions, capability checks, or namespace ownership rules. Therefore it is not justified to claim either host-admin-only reachability or ordinary-user reachability.

`NamespaceScopedPrivilege=UNKNOWN` because the supplied data does not establish that all required actions, including VDUSE device creation, configuration, activation, and network-device opening, can be completed solely with attacker-obtainable namespace-scoped capabilities.

No network packet trigger is shown. No special physical hardware is required. No race or timing condition is involved. The vulnerable state is deterministic once an invalid VDUSE configuration is accepted.

## 4. Primitive and severity interpretation

The exact primitive is invalid configuration acceptance followed by a NULL-pointer dereference in the virtio split-ring path.

A zero `vq_align` is accepted because the old validation only rejected values greater than `PAGE_SIZE`. The split-ring helpers use `align - 1` as an alignment mask. With zero alignment, ring layout calculation becomes invalid, the used-ring pointer remains NULL, and later virtio-net activation dereferences it.

This is not an active structured-object UAF, fixed stale storage issue, double release, refcount mutation, ownership violation, or semantic security-boundary bypass. It is a deterministic invalid-state crash path.

The demonstrated consequence is local kernel crash or denial of service. A privilege escalation, information disclosure, integrity violation, arbitrary read or write, controlled object reuse, or guest-to-host boundary escape is not supported by the patch or trace.

`PrimitiveClass=CLASS_C` is appropriate because the behavior is crash or DoS from invalid state without an independently useful corruption primitive. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` are appropriate because no unresolved concrete lifetime, ownership, authorization, or corruption leverage is established.

Operationally, this should be handled as a local VDUSE configuration validation defect. It may warrant normal patching where VDUSE is enabled and exposed to delegated management processes, but the supplied evidence does not justify Important-class handling.

## 5. One-sentence report phrase

An invalid VDUSE virtqueue alignment value can cause virtio split-ring initialization to leave the used-ring pointer NULL, allowing activation of the resulting virtio-net device to trigger a local kernel crash or denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch and trace establish a deterministic NULL-pointer dereference only. No UAF, write primitive, ownership violation, authorization bypass, remote trigger, or plausible exploitation mechanism beyond denial of service is demonstrated.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: vduse: validate virtqueue alignment [ Upstream
Commit: c3c3b0839a1197530cc18f535062fc84dbdfc885
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3c3b0839a1197530cc18f535062fc84dbdfc885

Changed files:
  drivers/vdpa/vdpa_user/vduse_dev.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=c3c3b0839a1197530cc18f535062fc84dbdfc885

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

The original Linux kernel CVE announcement for CVE-2026-97989 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97989

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:L/PR:H/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: 1

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).