[CVE-2026-97994][MODERATE REGULAR] vhost/vdpa: reject VRING_NUM larger than device max [ Upstream

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

CVE: CVE-2026-97994
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vhost/vdpa: reject VRING_NUM larger than device max [ Upstream
Commit: 1d09201d81b7d3e276860cc7b7dbf6c6cbe8e9b4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1d09201d81b7d3e276860cc7b7dbf6c6cbe8e9b4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97994
Analysis date: Sat, 26 Sep 2026 14:02:55 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97994 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97994

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-97994	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97994 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:L/I:L/A:H';CWE-125;*CWE-20;CWE-367;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'An out of bounds descriptor read in the vhost vdpa backend can occur because VHOST_SET_VRING_NUM accepts a queue size larger than the device maximum. With vdpa_sim the worker can walk beyond the mapped descriptor ring through vringh IOTLB handling. This produces a KASAN reported 16 byte out of bounds read and can crash the host kernel. For the CVSS the PR:L is selected because exploitation requires a local process with access to a /dev/vhost-vdpa device. The issue is not directly network reachable. The demonstrated impact is local denial of service. The out of bounds read and user supplied ring metadata warrant manual review for possible limited confidentiality or integrity effects in backend specific paths.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	READ KASAN OOB LOCK HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied. The supplied evidence establishes an out of bounds read and host kernel DoS potential, but does not establish disclosure, an out of bounds write, controlled corruption, lifetime violation, or a security-boundary bypass.

2. Signal breakdown

* +1 Reliable kernel crash or strong DoS. The supplied context reports that the vDPA worker can read past the mapped descriptor ring and that KASAN detects the invalid access. A production kernel may fault or crash when invalid descriptor access reaches an unmapped or invalid IOTLB area.
* +1 Weak indirect corruption candidate. A local vhost-vDPA user controls an oversized queue configuration and descriptor ring metadata, and kernel worker code consumes descriptors beyond the intended ring boundary. This is a concrete invalid structured descriptor interpretation, but not a demonstrated write or disclosure primitive.

Important non-awarded signals:

* +0 Controlled reclaim is not demonstrated.
* +0 Arbitrary or directed kernel write is not demonstrated.
* +0 Confidentiality is not awarded. The patch demonstrates an internal out of bounds read, but no path returning read data to userspace, network, guest, or device-visible output is established.
* +0 Integrity is not awarded. No kernel write, descriptor-controlled write target, or modification of protected state is established.
* +0 Remote reachability is not established. The vulnerable operation is an ioctl on a local /dev/vhost-vdpa device.
* +0 Local unprivileged trigger is not awarded. The input only establishes a process with access to /dev/vhost-vdpa, not that an ordinary unprivileged user receives such access.
* +0 Strong semantic reinterpretation is not awarded. The queue-size validation bug causes invalid bounds, but does not establish that data validated under one active security-relevant semantic domain is later consumed as another domain.
* +0 No privilege penalty is applied. Access control for the vhost-vDPA character device is not resolved by the supplied patch.
* +0 No niche subsystem penalty is applied. vDPA may be specialized, but the input does not establish that it is difficult for an authorized device user to instantiate or exercise.
* +0 No separate availability point is awarded. The potential crash is already counted once.

3. Reachability analysis

The evaluated attacker is a local userspace process that already has access to a /dev/vhost-vdpa device node. Such a process can invoke VHOST_SET_VRING_NUM and configure a power-of-two ring size that exceeds the backend device maximum in the vulnerable implementation.

The supplied evidence does not establish whether device-node access requires host root, a host-admin-equivalent capability, membership in a delegated virtualization group, a service account, or another access-control mechanism. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

The complete trigger requires a configured vDPA backend and an accessible vhost-vDPA device. vdpa_sim is specifically identified as a backend where the worker can walk beyond the mapped descriptor ring. The patch does not establish that all required device creation, backend provisioning, and device-node access can be performed in an attacker-created namespace. NamespaceScopedPrivilege is therefore UNKNOWN.

This is not directly network reachable. A remote guest or network peer is not shown to be able to independently open the character device, issue VHOST_SET_VRING_NUM, or configure the host-side vhost-vDPA queue.

No timing race is required for the main oversized-queue condition. The patch additionally copies the complete vring state once, preventing inconsistent use of separately fetched userspace index and size values, but the supplied evidence does not establish a separate exploitable TOCTOU consequence.

4. Primitive and severity interpretation

The directly established primitive is a read beyond the mapped descriptor ring in the vringh IOTLB path after an oversized VHOST_SET_VRING_NUM configuration is accepted. The observed access is a 16-byte out of bounds read corresponding to one vring descriptor.

This is not a UAF, double release, refcount corruption, stale active-object use, or ownership violation. There is no evidence that the worker writes beyond the ring, that read data is disclosed, or that attacker-controlled data is reused as an active kernel object with controlled callbacks, pointers, or lifetime fields.

The issue is CLASS_C because the demonstrated behavior is invalid-state processing leading primarily to a kernel fault or denial of service. The practical consequence supported by the supplied context is a local host kernel crash or DoS for a process that can access the vhost-vDPA device. Limited confidentiality or integrity consequences remain a backend-specific possibility requiring manual inspection, but they are not established by this patch.

ImportantCandidate is NO because no meaningful exploitation leverage beyond the invalid read and crash path is demonstrated. AutoDowngradeAllowed is YES because the known primitive is constrained to an out of bounds read with no established disclosure, write, UAF, controlled reclaim, or security-boundary bypass.

Likely operational severity is ordinary Moderate. It should be manually sampled for backend-specific behavior, especially if the affected deployment exposes vhost-vDPA device access to non-host-admin virtualization services.

5. One-sentence report phrase

A local process with access to a vhost-vDPA device can configure a queue larger than the backend maximum, causing an out of bounds descriptor read in the vringh IOTLB worker path and potentially crashing the host kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The demonstrated primitive is an out of bounds read with potential host DoS, and backend-specific descriptor handling should be checked for any subsequent write, read-back, guest-visible disclosure, or device-specific memory access effect.

7. Call-site confidence

Call-site confidence: medium

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

Patch: vhost/vdpa: reject VRING_NUM larger than device max [ Upstream
Commit: 1d09201d81b7d3e276860cc7b7dbf6c6cbe8e9b4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1d09201d81b7d3e276860cc7b7dbf6c6cbe8e9b4

Changed files:
  drivers/vhost/vdpa.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=1d09201d81b7d3e276860cc7b7dbf6c6cbe8e9b4

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

The original Linux kernel CVE announcement for CVE-2026-97994 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97994

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: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:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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).