[CVE-2026-74355][MODERATE 7.0] iommu/vt-d: Fix RB-tree corruption in probe error path [ Upstream

[CVE-2026-74355][MODERATE 7.0] iommu/vt-d: Fix RB-tree corruption in probe error path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74355
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iommu/vt-d: Fix RB-tree corruption in probe error path [ Upstream
Commit: f5102e0fc3c6dc8685549891a96e4589fdb3e211
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f5102e0fc3c6dc8685549891a96e4589fdb3e211
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74355
Analysis date: Sun, 16 Aug 2026 00:20:53 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum. Strong Important candidate only if further analysis shows controlled RB tree corruption or an IOMMU isolation bypass
Manual review required: YES

Summary:
An Intel VT-d probe error path can remove an RB node that was never inserted, corrupting the IOMMU device RB tree and potentially causing kernel instability or DoS, with limited paranoid concern for IOMMU isolation impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74355 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74355

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-2026-74355	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:L/I:L/A:H';CWE-665;CWE-763;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'An Intel IOMMU probe error path can call rb_erase on info node even when the node was never inserted into the device RB tree. This can corrupt the IOMMU device tracking tree when a device does not support ATS and a later probe step fails. The issue is local and hardware or device management dependent, not network reachable. For the CVSS the PR:L is used for paranoid scoring because delegated device management, service accounts, reduced capability root, or containerized admin paths may be enough to influence probe or bind failure flows in some deployments. Impact is at least denial of service through corrupted kernel state or crash. In worst case it may allow limited confidentiality or integrity impact because the corrupted structure belongs to the IOMMU device domain tracking path, but no direct arbitrary write or proven privilege escalation primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum. Strong Important candidate only if further analysis shows controlled RB tree corruption or an IOMMU isolation bypass (with actual score 4)	YES	DANGER INIT SIMPLEFIX ERRORPATH HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum. Strong Important candidate only if further analysis shows controlled RB tree corruption or an IOMMU isolation bypass**::

## 2. Signal breakdown

Triggered signals:

* Firmware-mediated external influence: +1
  The trigger depends on device capability state, specifically a device without ATS support, plus a later probe failure.

* Memory corruption, Weak/indirect corruption candidate: +1
  `rb_erase()` is called on an RB node that was never inserted. This can corrupt the Intel IOMMU device RB tree, but the patch does not show attacker-controlled payload, target selection, or a strong overwrite primitive.

* Privileged kernel/device-management memory corruption path: +1
  The corrupted object is in the Intel VT-d IOMMU device tracking path, which is a highly trusted kernel subsystem related to device-domain accounting.

* Reliable kernel crash / strong DoS: +1
  RB-tree corruption in device tracking can plausibly lead to kernel crashes, broken probe paths, or unstable IOMMU/device state.

Paranoid-only signals:

* Weak LPE concern: +1
  The corruption is in IOMMU device-domain tracking, so limited security impact beyond DoS is worth manual review, although no direct LPE primitive is demonstrated.

* Confidentiality impact plausible: +1
  Only for paranoid scoring, because IOMMU metadata corruption could theoretically affect DMA isolation accounting.

* Integrity impact plausible: +1
  Only for paranoid scoring, because corrupted IOMMU device-domain tracking could theoretically affect isolation or device assignment correctness.

Subtractions:

* Hard or unreliable race / special condition required: -1
  Triggering requires a specific probe error path after ATS insertion was skipped.

* Corruption primitive highly constrained or metadata-only: -1
  The corrupted object is kernel RB-tree metadata, and there is no evidence of attacker-controlled data overwrite.

## 3. Reachability analysis

This is not network reachable. The realistic trigger is local, firmware-mediated, or device-management mediated. A device must not support ATS, and a later Intel IOMMU probe step must fail so that the error path reaches `device_rbtree_remove()` for a node that was never inserted.

In typical deployments, directly forcing this path likely requires administrative control over device binding, hotplug, driver probing, or hardware state. However, delegated device management, reduced-capability service accounts, containerized admin workflows, or firmware/device behavior may reduce the practical privilege barrier in some environments. The path is not broadly user-triggerable like a syscall or socket API.

Call-site confidence: high. The patch shows both the broken remove helper and the initialization site in `intel_iommu_probe_device()`.

## 4. Severity interpretation

This is stronger than an ordinary low-risk cleanup because it can corrupt a kernel RB tree in the IOMMU device tracking path. Conservative handling is borderline Moderate with manual review recommended.

Realistically, the demonstrated impact is most likely DoS or unstable device/IOMMU state. Theoretical confidentiality or integrity impact is possible only in the paranoid interpretation due to the IOMMU domain tracking context. The patch does not demonstrate arbitrary write, controlled object replacement, UAF reclaim, callback control, or a proven privilege escalation path.

## 5. One-sentence report phrase

An Intel VT-d probe error path can remove an RB node that was never inserted, corrupting the IOMMU device RB tree and potentially causing kernel instability or DoS, with limited paranoid concern for IOMMU isolation impact.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is metadata corruption in a security-sensitive IOMMU device-management path. It is not enough for an Important classification by itself, but it should not be auto-closed without checking whether probe failure can be influenced by device firmware, hotplug, passthrough, or delegated device-management scenarios.

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

Patch: iommu/vt-d: Fix RB-tree corruption in probe error path [ Upstream
Commit: f5102e0fc3c6dc8685549891a96e4589fdb3e211
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f5102e0fc3c6dc8685549891a96e4589fdb3e211

Changed files:
  drivers/iommu/intel/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=f5102e0fc3c6dc8685549891a96e4589fdb3e211

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

The original Linux kernel CVE announcement for CVE-2026-74355 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74355

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:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  Paranoid ActionableScore: 5

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).