[CVE-2026-74361][MODERATE 7.0] nvme: fix FDP fdpcidx bounds check [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-74361
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nvme: fix FDP fdpcidx bounds check [ Upstream
Commit: 5e406928404d67a8da8aa3ae21732e1ea1a04118
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e406928404d67a8da8aa3ae21732e1ea1a04118
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74361
Analysis date: Sun, 16 Aug 2026 04:05:28 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
An off-by-one bounds check in the NVMe FDP host path can accept an invalid FDP configuration index from a malicious or faulty controller, potentially causing incorrect block-layer FDP registration or limited out-of-bounds descriptor access in a storage-adjacent attack model.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74361 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74361

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: NO

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-2026-74361	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-193;CWE-125;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7.6';DESCR 'An off by one bounds check in the NVMe FDP host path can accept fdp_idx equal to NUMFDPC plus 1 instead of rejecting it. A malicious or faulty NVMe controller can make the host use an invalid FDP configuration index, which may lead to an out of bounds read of FDP configuration data or incorrect block layer FDP stream registration. For the CVSS the PR:N is used in the paranoid score because the attacker does not need a local account on the host if they control a reachable NVMe controller or storage fabric endpoint. The issue is not Internet remote in the usual deployment model and is best treated as adjacent network or device reachable. Impact is at least reliability degradation or denial of service. In the paranoid view, limited confidentiality or integrity impact is kept because the bug class is an invalid bounds check in host parsing of controller supplied data.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB SIMPLEFIX NVME IMPROVEONLY LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The invalid `fdp_idx` value is tied to NVMe FDP controller supplied parameters or behavior.
* Memory corruption, weak/indirect corruption candidate: +1. This is an off-by-one bounds check in a host parser path. It may allow an invalid FDP configuration index, but the patch does not show an OOB write or attacker-controlled overwrite.
* Availability impact realistic: +1. Incorrect FDP registration or invalid descriptor access can plausibly break device setup or cause a host-side fault, but no reliable crash primitive is shown.
* Important filesystem/storage path: +1. The bug is in the NVMe host block/storage path and affects FDP parameter registration with the block layer.

Paranoid additions:

* Confidentiality impact plausible: +1. A limited OOB read of adjacent FDP configuration data is technically plausible from the invalid index class, but no disclosure path is demonstrated.
* Integrity impact plausible: +1. Incorrect FDP stream or placement registration could affect storage behavior, but this is not a demonstrated cross-file or page-cache corruption primitive.

Not awarded:

* No remote network-triggerable +2. NVMe/TCP or NVMe-oF may make this storage-adjacent, but the usual model is controller or fabric endpoint influence, not arbitrary Internet reachability.
* No strong memory corruption +2. The patch shows a bounds validation fix, not OOB write, UAF, double free, type confusion, or arbitrary write.
* No privilege escalation +2. There is no demonstrated LPE primitive.
* No Dirty-Pipe-like or page-cache corruption bonus. The patch does not show shared page, COW, reflink, or externally owned page corruption.

## 3. Reachability analysis

A malicious, faulty, or compromised NVMe controller or storage fabric endpoint can plausibly influence the FDP index or FDP configuration data consumed by the host. A local unprivileged Linux user is not the typical direct trigger unless they can attach or control such a device or storage endpoint. Namespaces and containers do not normally reduce the privilege requirement for attaching NVMe hardware or configuring NVMe-oF targets, but cloud or virtualization environments with attacker-controlled virtual NVMe devices could make the scenario more relevant.

The affected path is not an ordinary packet-processing path and should not be treated as Internet remote. It is storage-adjacent and device-mediated. FDP itself is an optional NVMe feature, so exposure depends on controller capability and whether FDP registration is used.

Call-site confidence: medium. The patch gives the vulnerable check and function context, but not all downstream FDP descriptor users.

## 4. Severity interpretation

This is stronger than an ordinary Low correctness issue because it is a host-side parser bug for controller supplied storage metadata in an important block subsystem. Conservatively it is a borderline manual-review issue because the demonstrated primitive is an invalid index with likely availability impact, not proven memory corruption.

The paranoid interpretation reaches Actionable Moderate because an off-by-one in NVMe FDP descriptor selection could plausibly become limited OOB read or incorrect storage registration. However, current evidence does not support classifying it as a Strong Important candidate without additional proof of OOB write, host memory disclosure, persistent storage corruption, or privilege escalation.

## 5. One-sentence report phrase

An off-by-one bounds check in the NVMe FDP host path can accept an invalid FDP configuration index from a malicious or faulty controller, potentially causing incorrect block-layer FDP registration or limited out-of-bounds descriptor access in a storage-adjacent attack model.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a storage host parser bounds bug with firmware or controller mediated input and possible OOB descriptor access, but the supplied patch does not demonstrate a strong corruption primitive, direct privilege escalation, or Internet remote reachability.

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

Patch: nvme: fix FDP fdpcidx bounds check [ Upstream
Commit: 5e406928404d67a8da8aa3ae21732e1ea1a04118
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e406928404d67a8da8aa3ae21732e1ea1a04118

Changed files:
  drivers/nvme/host/core.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=5e406928404d67a8da8aa3ae21732e1ea1a04118

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

The original Linux kernel CVE announcement for CVE-2026-74361 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74361

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 7.6

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: 6

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).