[CVE-2026-72305][MODERATE REGULAR] VDUSE: avoid leaking information to userspace [ Upstream

[CVE-2026-72305][MODERATE REGULAR] VDUSE: avoid leaking information to userspace [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72305
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: VDUSE: avoid leaking information to userspace [ Upstream
Commit: fde25641cbddd0c084e3320d08f755e7e6acfae5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fde25641cbddd0c084e3320d08f755e7e6acfae5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72305
Analysis date: Sun, 16 Aug 2026 04:56:25 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / Actionable Moderate only if VDUSE is delegated to low privilege users
Manual review required: YES

Summary:
VDUSE may leak stale kernel memory to a local userspace backend because bounce and coherent pages were allocated without forced zeroing before userspace could observe them.

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

The original Linux kernel CVE announcement for CVE-2026-72305 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72305

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: 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
======================================================================

CVE-2026-72305	MODERATE	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:H/I:N/A:N';*CWE-200;CWE-908;CWE-665;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'VDUSE can leak kernel information to userspace because bounce pages and coherent allocations were not forced to be zeroed before they could be mapped or observed by a userspace VDUSE process. The affected bounceing path is not necessarily page aligned, so unused bytes in the allocated page may contain stale kernel memory from prior use. For the CVSS the PR:L is used because triggering requires a local userspace context with access to the VDUSE device interface, but not necessarily full host administrative control in delegated or service based deployments. The issue is not network reachable and does not provide a write primitive. Impact is confidentiality only, with base C:L and paranoid C:H because stale kernel memory may expose sensitive data or kernel addresses. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate only if VDUSE is delegated to low privilege users (with actual score 3)	YES	SIMPLEFIX LEAK HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate only if VDUSE is delegated to low privilege users**::

## 2. Signal breakdown

Conservative signals:

* Local low privilege trigger in some deployments: +1
  A userspace VDUSE backend or process with access to the VDUSE device path can observe the affected mapped bounce or coherent buffers. This is not a pure remote issue.

* Confidentiality impact plausible: +1
  The patch explicitly states that unzeroed bounce pages can leak kernel information to userspace.

* Security boundary bypass concern: +1
  The bug crosses the kernel to userspace confidentiality boundary by exposing stale kernel memory through buffers that userspace can map or observe.

* Rare and configuration dependent subsystem: -1
  VDUSE is not a default exposed interface on ordinary systems and normally appears in virtualization or vDPA deployments.

Paranoid difference:

* The rare subsystem penalty is not applied in environments where VDUSE is intentionally deployed and delegated to a userspace backend service. In that case the issue is more actionable because the affected interface is part of the normal data path for that deployment.

No memory corruption, write primitive, UAF, OOB write, privilege escalation primitive, or network reachability is supported by the patch.

## 3. Reachability analysis

The bug is reachable by a local userspace process that can operate the VDUSE device interface or act as a VDUSE backend. In typical host deployments, creating or managing VDUSE devices may require administrative setup, so this is not universally unprivileged. However, practical deployments may delegate the backend process to a service account or containerized component, making PR:L a reasonable paranoid interpretation.

The path is not network reachable by itself. An external attacker would need a separate path to influence a local VDUSE backend or workload. The subsystem is not broadly default enabled for normal Linux systems, but it is relevant in virtualization and vDPA based storage or networking setups.

## 4. Severity interpretation

This behaves like an information disclosure issue, not memory corruption. The realistic impact is leakage of stale kernel memory contents into userspace because pages were not zeroed before being mapped or observed. The worst case is higher confidentiality impact if leaked bytes contain kernel pointers, secrets, or other sensitive data, but the patch does not support integrity impact, availability impact, arbitrary read, arbitrary write, or privilege escalation.

Overall this is an ordinary Moderate issue in generic systems, but it should not be blindly auto closed for products that expose VDUSE to non root service accounts or delegated virtualization components.

## 5. One-sentence report phrase

VDUSE may leak stale kernel memory to a local userspace backend because bounce and coherent pages were allocated without forced zeroing before userspace could observe them.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a kernel information leak across the kernel to userspace boundary, and practical severity depends heavily on whether VDUSE access is restricted to full host root or delegated to lower privilege backend processes.

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

Patch: VDUSE: avoid leaking information to userspace [ Upstream
Commit: fde25641cbddd0c084e3320d08f755e7e6acfae5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fde25641cbddd0c084e3320d08f755e7e6acfae5

Changed files:
  drivers/vdpa/vdpa_user/iova_domain.c
  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=fde25641cbddd0c084e3320d08f755e7e6acfae5

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

The original Linux kernel CVE announcement for CVE-2026-72305 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72305

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  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: 2
  Paranoid ActionableScore: 3

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).