[CVE-2026-74328][MODERATE 7.0] iommufd: Destroy the pages content after detaching from dmabuf [ Upstream

[CVE-2026-74328][MODERATE 7.0] iommufd: Destroy the pages content after detaching from dmabuf [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74328
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: iommufd: Destroy the pages content after detaching from dmabuf [ Upstream
Commit: 0507fcedbdcc87281ef8639c045fc9980363bbb6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0507fcedbdcc87281ef8639c045fc9980363bbb6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74328
Analysis date: Sat, 15 Aug 2026 06:24:12 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
iommufd may destroy iopt_pages state before a DMABUF is fully detached, allowing invalidation callbacks to access destroyed mutex or lifetime-managed fields and causing at least local DoS with possible memory-lifetime corruption requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-74328 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74328

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-2026-74328	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'iommufd releases pages content in the wrong order for DMABUF backed mappings. The dmabuf invalidation callbacks may still run during detach and may still use fields inside the iopt_pages object, including synchronization state such as pages mutex, after those fields were already destroyed or references were dropped. This creates a lifetime ordering race and a use after destroy or use after free candidate in a local kernel interface. For the CVSS the PR:L is used because a local process with access to iommufd and a DMABUF backed mapping may trigger the detach path, even if many deployments restrict this to virtualization or device assignment services. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact because stale callback access to released kernel objects is a memory corruption candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)  SKIP CVE-2026-74328 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 71db84a092c399f434976d0522e848e9803cd51a YES  NO NO unknown 	MAYBE	SIMPLEFIX KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local trigger: +1. A local process with access to iommufd and a DMABUF backed mapping can potentially reach the detach and release path.
* Memory corruption, weak or indirect corruption candidate: +1. The patch fixes destroyed object content being reachable through DMABUF invalidation callbacks, but no controlled reclaim or overwrite primitive is shown.
* Real lifetime corruption: +1. The bug is an object lifetime ordering issue involving mmdrop, mutex_destroy, put_task_struct, free_uid, and callback execution during detach.
* Reliable kernel crash / strong DoS: +1. Use of a destroyed mutex or dropped lifetime references can plausibly lead to WARN, Oops, or kernel crash.

Paranoid additional signals:

* Weak LPE concern: +1. Stale callback access to released kernel state is a manual review candidate, although no concrete attacker controlled reuse is demonstrated.
* Confidentiality impact plausible: +1. Only for paranoid scoring, because lifetime corruption in kernel objects may expose state if the stale access is more than a crash.
* Integrity impact plausible: +1. Only for paranoid scoring, because stale callback access could potentially corrupt kernel state depending on callback behavior and object reuse.

Not applied:

* Remote reachable: +0. This is not network reachable.
* Strong LPE plausibility: +0. No reclaim, arbitrary write, type confusion, or controlled object replacement is demonstrated.
* Requires full admin penalty: not applied as -2. iommufd and DMABUF access may be delegated to virtualization or device assignment processes and should not always be treated as full host root.
* Hard race penalty: not applied conservatively. The issue is an ordering bug in the detach path, not necessarily a narrow timing-only race.
* Call-site confidence: medium. The release path and ordering are visible, but the exact invalidation callback body is not included.

## 3. Reachability analysis

The bug is reachable through a local kernel device management path involving iommufd pages backed by DMABUF. A realistic trigger requires a process that can create or receive the relevant iommufd and DMABUF objects and cause detach or release of the mapping. This is commonly associated with virtualization, VFIO, GPU, accelerator, or delegated device workflows rather than ordinary shell-only local use.

Namespaces and containers can matter. If a container, sandboxed service, or non-root virtualization process is delegated the relevant device file descriptors, PR is closer to local low privilege in practical triage terms. If only host root can create the relevant objects, the conservative risk is lower. The path is not remotely reachable and is not a common packet or filesystem data path.

## 4. Severity interpretation

This is more than an ordinary cleanup bug because the destroyed content may still be used by asynchronous DMABUF invalidation callbacks. The conservative interpretation is a local DoS with weak memory lifetime corruption, giving a borderline score that still deserves review. The paranoid interpretation treats the stale callback access as a UAF or use-after-destroy candidate in a privileged DMA and IOMMU management subsystem, which makes it a Strong Important candidate for manual triage.

Theoretical memory corruption potential exists due to lifetime ordering, but the patch does not demonstrate attacker controlled reclaim, arbitrary write, type confusion, or a reliable privilege escalation chain. Therefore the main result should not claim proven LPE, but it should not be auto-closed.

## 5. One-sentence report phrase

iommufd may destroy iopt_pages state before a DMABUF is fully detached, allowing invalidation callbacks to access destroyed mutex or lifetime-managed fields and causing at least local DoS with possible memory-lifetime corruption requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This involves a real lifetime ordering issue in iommufd plus DMABUF callback interaction. The likely minimum impact is local kernel crash, but stale callback access to released kernel state is sufficiently security-relevant to require manual review.

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

Patch: iommufd: Destroy the pages content after detaching from dmabuf [ Upstream
Commit: 0507fcedbdcc87281ef8639c045fc9980363bbb6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0507fcedbdcc87281ef8639c045fc9980363bbb6

Changed files:
  drivers/iommu/iommufd/pages.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=0507fcedbdcc87281ef8639c045fc9980363bbb6

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

The original Linux kernel CVE announcement for CVE-2026-74328 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74328

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:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 7

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).