[CVE-2026-64152][LOW] iommu: Handle unmap error when iommu_debug is enabled [ Upstream

[CVE-2026-64152][LOW] iommu: Handle unmap error when iommu_debug is enabled [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64152
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iommu: Handle unmap error when iommu_debug is enabled [ Upstream
Commit: 0cd028806efc148a75d4acf711d21db335a89661
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0cd028806efc148a75d4acf711d21db335a89661
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64152
Analysis date: Sun, 19 Jul 2026 15:57:55 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
An IOMMU map error path could perform debug unmap tracking without a matching debug map record after partial mapping failure, causing debug-state malfunction or possible DoS only when IOMMU debug tracking is enabled.

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

The original Linux kernel CVE announcement for CVE-2026-64152 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64152

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-2026-64152	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-703;CWE-754;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'An error path in iommu_map_nosync can call iommu_unmap after a partial IOMMU mapping failure while iommu_debug tracking has not recorded the matching map operation. With IOMMU_DEBUG_PAGEALLOC or similar debug tracking enabled, this can create unmatched map/unmap state and may lead to warnings, debug malfunction, or denial of service in the mapping error path. For the CVSS the PR:L is used for the paranoid view because some deployments may delegate device or VFIO access to a local user or service account, allowing indirect access to IOMMU mapping paths. Reliable triggering is still high complexity because it depends on a partial map failure and a debug configuration. The issue is not network reachable and does not show a concrete information leak, UAF, OOB access, or arbitrary write primitive. Impact is best treated as availability only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-64152 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: ccc21213f013834b484cdcc738e282f963fcfc97 YES  NO NO unknown 	MAYBE	LOCK ERRORPATH 	-	-	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:

* Availability impact realistic: +1
  The bug can create unbalanced `iommu_debug` map/unmap tracking on a partial map failure path. The practical impact is warnings, debug-tracking malfunction, or possible DoS in debug configurations.

Paranoid-only signal:

* Local delegated device path concern: +1
  In some deployments, VFIO or similar device access may be delegated to a local user or service account, allowing indirect interaction with IOMMU mapping paths.

Subtracted signals:

* Requires admin/root/device-management privileges in typical deployments: -2
  Normal triggering usually requires privileged kernel/device/IOMMU mapping operations, not a general unprivileged syscall path.

* Hard or unreliable trigger condition: -1
  The issue requires a partial IOMMU map failure in the error path.

* Non-default/debug configuration: -1
  The problematic tracking path depends on `IOMMU_DEBUG_PAGEALLOC` or similar debug tracking being enabled.

Not applied:

* No generic memory corruption signal.
  The patch does not show UAF, double free, OOB write, arbitrary write, type confusion, or stale object reuse.

* No privilege escalation signal.
  There is no supported LPE primitive.

* No confidentiality or integrity signal.
  The bug is about unmatched debug tracking around map/unmap rollback, not disclosure or data modification.

## 3. Reachability analysis

Typical reachability is local and privileged through kernel IOMMU mapping paths used by drivers, DMA, VFIO, or device-management code. It is not network reachable. Namespaces or containers do not normally expose this path unless a device or VFIO-style interface is explicitly delegated. Even then, reliable triggering requires both debug tracking enabled and a partial map failure, so exploitation conditions are narrow.

Call-site confidence: high. The provided patch includes the relevant caller path in `iommu_map_nosync()` and the changed rollback behavior.

## 4. Severity interpretation

This behaves like a low-end Moderate or Low-like reliability bug, not an Important-class vulnerability. The theoretical worst case is availability impact from malformed debug accounting during rollback. Realistic exploitation evidence is weak because the issue is debug-config dependent, error-path dependent, and lacks a concrete memory-corruption or privilege-escalation primitive.

## 5. One-sentence report phrase

An IOMMU map error path could perform debug unmap tracking without a matching debug map record after partial mapping failure, causing debug-state malfunction or possible DoS only when IOMMU debug tracking is enabled.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for security triage unless the evaluated product enables IOMMU debug tracking in production and delegates VFIO or device access to untrusted local users.

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

Patch: iommu: Handle unmap error when iommu_debug is enabled [ Upstream
Commit: 0cd028806efc148a75d4acf711d21db335a89661
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0cd028806efc148a75d4acf711d21db335a89661

Changed files:
  drivers/iommu/iommu.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=0cd028806efc148a75d4acf711d21db335a89661

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

The original Linux kernel CVE announcement for CVE-2026-64152 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64152

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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).