[CVE-2026-74312][MODERATE 7.0] vhost/vdpa: validate virtqueue index in mmap and fault paths [ Upstream

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

CVE: CVE-2026-74312
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vhost/vdpa: validate virtqueue index in mmap and fault paths [ Upstream
Commit: 0f310bac6db9bd3bb1655707d692d9d2a86eeb17
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f310bac6db9bd3bb1655707d692d9d2a86eeb17
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74312
Analysis date: Sat, 15 Aug 2026 04:05:53 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local process with access to a vhost/vdpa file descriptor can pass an out-of-range mmap offset that reaches driver-specific virtqueue notification callbacks, potentially causing invalid PFN remaps and kernel DoS, with limited C/I impact defensible in the worst case.

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

The original Linux kernel CVE announcement for CVE-2026-74312 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74312

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-2026-74312	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-129;*CWE-20;CWE-125;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'vhost/vdpa mmap and fault paths used vma vm_pgoff as a virtqueue index without validating it against the number of configured queues. A local process with access to a vhost/vdpa file descriptor could pass an out of range mmap offset and reach driver specific get_vq_notification callbacks with an invalid queue index. For the CVSS the PR:L is used for the paranoid score because triggering requires local access to the vhost/vdpa device or a service account that can operate it, but not necessarily full host administrator privileges. The issue is not network reachable and is triggered through a local mmap or fault path rather than packet traffic. Impact is at least local denial of service via invalid notification area handling and kernel crash. In the worst defensible case it may allow limited confidentiality or integrity impact if an out of bounds callback read leads to an unintended PFN remap. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	READ OOB DANGER IMPROVEONLY KERNEL_PANIC_PLUS_UAF LINUS MEMORY  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged or reduced-privilege trigger: +1
  Triggering requires local access to a vhost/vdpa file descriptor or a service context that can operate it. This is PR:L-like in practical triage, not necessarily full host root.

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is an unchecked virtqueue index reaching driver-specific get_vq_notification callbacks. This is an out-of-bounds object selection risk, but the patch does not show an attacker-controlled write, reclaim, type confusion, or arbitrary memory access primitive.

* Reliable kernel crash / strong DoS: +1
  Source inspection and the commit context support invalid notification area handling, invalid PFN remap, SIGBUS, or kernel crash/DoS.

* Privileged kernel/device-management memory corruption path: +1
  The affected path is in vhost/vdpa virtualization/device-management mmap and fault handling, with possible invalid PFN remapping into userspace.

Paranoid additional signals:

* Confidentiality impact plausible: +1
  Limited confidentiality impact is plausible if an out-of-range callback returns an unintended notification area or PFN that becomes observable through mmap behavior.

* Integrity impact plausible: +1
  Limited integrity impact is plausible if invalid PFN remapping exposes or maps a wrong device/kernel-related region, although no strong write primitive is demonstrated.

Signals not awarded:

* No remote/network-triggerable signal. The path is mmap/fault on a local device fd.
* No strong LPE plausibility. There is no demonstrated reclaim, controlled overwrite, callback control, refcount takeover, or arbitrary write.
* No strong generic memory corruption +2. The primitive is unchecked index/object selection, not proven OOB write or UAF.
* No rare-subsystem penalty applied in the main score because vhost/vdpa is niche but reachable through ordinary local interfaces on systems where it is deployed.

## 3. Reachability analysis

The likely attacker is a local process with access to a vhost/vdpa device file descriptor, such as a VM manager, qemu-like service account, containerized virtualization helper, or another delegated device-management context. Typical desktop or server systems without vDPA configured are not exposed. Namespaces and containers matter because access may be delegated to a reduced-capability root or service user, so treating this as full PR:H would understate practical risk. The issue is not packet-triggered and is not remotely reachable by itself.

Call-site confidence: high. The patch shows both affected call sites, vhost_vdpa_mmap and vhost_vdpa_fault, and the shared helper now validates the index before calling the driver callback.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an ordinary low-risk validation bug. The realistic impact is local DoS through invalid virtqueue notification handling or invalid PFN remapping. The theoretical higher concern is limited C/I impact from out-of-bounds callback selection and unintended PFN exposure, but the patch does not support a strong privilege-escalation primitive. It should not be auto-closed without manual review because the final impact depends on driver-specific get_vq_notification implementations.

## 5. One-sentence report phrase

A local process with access to a vhost/vdpa file descriptor can pass an out-of-range mmap offset that reaches driver-specific virtqueue notification callbacks, potentially causing invalid PFN remaps and kernel DoS, with limited C/I impact defensible in the worst case.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a virtualization mmap/fault path with unchecked object indexing and possible invalid PFN remapping. The exact impact depends on driver-specific get_vq_notification callbacks, so the bug should be treated as Actionable Moderate rather than auto-closed.

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

Patch: vhost/vdpa: validate virtqueue index in mmap and fault paths [ Upstream
Commit: 0f310bac6db9bd3bb1655707d692d9d2a86eeb17
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f310bac6db9bd3bb1655707d692d9d2a86eeb17

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=0f310bac6db9bd3bb1655707d692d9d2a86eeb17

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

The original Linux kernel CVE announcement for CVE-2026-74312 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74312

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: 4
  Paranoid ActionableScore: 6

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 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).