[CVE-2026-64186][LOW] iommu/amd: Remove latent out-of-bounds access in IOMMU debugfs [ Upstream

[CVE-2026-64186][LOW] iommu/amd: Remove latent out-of-bounds access in IOMMU debugfs [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64186
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iommu/amd: Remove latent out-of-bounds access in IOMMU debugfs [ Upstream
Commit: 488d2c76bd9f78433a70690d1054bfae3d39a407
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=488d2c76bd9f78433a70690d1054bfae3d39a407
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64186
Analysis date: Sun, 19 Jul 2026 13:45:20 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
AMD IOMMU debugfs used unsigned parsing for signed offsets, creating a latent negative-offset OOB access concern, but practical exploitation is unlikely because privileged debugfs access is required and existing checks already constrained the path.

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

The original Linux kernel CVE announcement for CVE-2026-64186 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64186

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-2026-64186	LOW	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:L';CWE-681;CWE-190;CWE-125;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:N';BEST CVSS score: '3';DESCR 'AMD IOMMU debugfs offset parsing used an unsigned parser while storing the result in signed int variables. A very large parsed value could theoretically become a negative offset and later lead to an out-of-bounds MMIO or capability register access, but the existing code had multiple practical guards including the short input limit and later read side checks. For the CVSS the PR:H is used because reliable triggering requires privileged local write access to AMD IOMMU debugfs files. The issue is not network reachable and is not triggered by normal packet or device traffic. Impact is best treated as no demonstrated current impact, with only a paranoid low impact scenario for limited out-of-bounds read or local fault if surrounding protections changed.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	WRITE OOB IMPROVEONLY DEBUGFS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Weak or latent OOB access concern: +1 paranoid only. The patch addresses signedness parsing that could theoretically create a negative offset for AMD IOMMU debugfs MMIO or capability access.
* Requires admin/root/debugfs access in typical deployments: -2. Reliable triggering requires privileged local write access to AMD IOMMU debugfs files.
* Rare and difficult-to-reach subsystem/configuration: -1. This requires AMD IOMMU debugfs exposure and is not a default unprivileged interface.

Not triggered:

* No remote reachability.
* No local unprivileged trigger.
* No demonstrated UAF, double free, OOB write, arbitrary write, type confusion, or controlled memory corruption.
* No strong DoS shown.
* No practical privilege escalation path shown.
* No meaningful confidentiality or integrity impact in the conservative interpretation.

## 3. Reachability analysis

The affected path is local debugfs control for AMD IOMMU debugging. In normal deployments, debugfs is root-accessible and often not mounted or not exposed to untrusted users. Containers and namespaces usually do not make this reachable unless the host deliberately exposes debugfs or grants elevated privileges. The commit explicitly states that several existing guards already prevented practical exploitation, including input length limits, unsigned promotion checks, and show-side rejection of negative offsets.

Call-site confidence: high. The provided diff includes the write handlers and the described downstream show-handler behavior.

## 4. Severity interpretation

This behaves like a latent hardening fix rather than an actionable vulnerability. The theoretical issue is signedness-related negative offset handling, but the patch and commit message indicate that the current implementation already had multiple practical protections. The realistic impact is no demonstrated security impact. The paranoid interpretation allows only a very low score for a possible limited OOB read or local fault if surrounding assumptions changed.

## 5. One-sentence report phrase

AMD IOMMU debugfs used unsigned parsing for signed offsets, creating a latent negative-offset OOB access concern, but practical exploitation is unlikely because privileged debugfs access is required and existing checks already constrained the path.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for practical triage unless external advisory data shows a real reachable OOB read, crash, or privilege boundary bypass.

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

Patch: iommu/amd: Remove latent out-of-bounds access in IOMMU debugfs [ Upstream
Commit: 488d2c76bd9f78433a70690d1054bfae3d39a407
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=488d2c76bd9f78433a70690d1054bfae3d39a407

Changed files:
  drivers/iommu/amd/debugfs.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=488d2c76bd9f78433a70690d1054bfae3d39a407

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

The original Linux kernel CVE announcement for CVE-2026-64186 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64186

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

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: 0
  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).