[CVE-2026-74386][MODERATE 7.0] nvmet-tcp: fix page fragment cache leak in error path [ Upstream

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

CVE: CVE-2026-74386
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nvmet-tcp: fix page fragment cache leak in error path [ Upstream
Commit: a43a9abc1ebf663f0aa56a729106f68dd9c77da6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a43a9abc1ebf663f0aa56a729106f68dd9c77da6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74386
Analysis date: Sat, 15 Aug 2026 07:56:39 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A network-reachable NVMe/TCP target can leak page fragment cache references when connections fail during queue allocation, allowing repeated failed connections to cause kernel memory exhaustion and denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-74386 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74386

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-2026-74386	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A page fragment cache leak in the NVMe TCP target queue allocation error path can occur when a connection is closed during nvmet_tcp_alloc_queue and the error path exits without draining queue pf_cache. A remote host on a reachable storage network can repeatedly open and close connections during allocation failure windows, causing leaked page fragments to accumulate over time and potentially exhaust kernel memory. For the CVSS the PR:N is used because no local account on the victim is required beyond reachability to the NVMe TCP target endpoint. The attack vector is treated as AV:A because NVMe TCP targets are normally deployed inside storage or data center networks rather than exposed to the public Internet. Impact is denial of service through memory exhaustion. There is no evidence of UAF, OOB access, arbitrary write, information disclosure, or privilege escalation in this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE SIMPLEFIX NVME LEAK ERRORPATH NETWORK LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  NVMe/TCP target is reachable over TCP when the target port is exposed to the attacker, though typically only on a storage or data-center network.

* Reliable kernel crash / strong DoS: +1
  The bug leaks a page fragment cache reference on each affected failed queue allocation. Repeated connection failures can lead to memory exhaustion.

* Important filesystem/storage path: +1
  The affected code is in the NVMe/TCP target path, which is a storage subsystem exposed to remote initiators in configured deployments.

* Availability impact realistic: +1 in paranoid score only
  Sustained repeated abuse can plausibly exhaust kernel memory and affect the whole system, but a single trigger is not expected to cause immediate failure.

* No generic memory corruption: +0
  The patch shows a resource leak, not UAF, double-free, OOB write, arbitrary write, type confusion, or page-cache corruption.

* No privilege escalation plausible: +0
  There is no supported LPE primitive in the patch context.

* No confidentiality or integrity impact: +0
  The bug leaks kernel memory resources but does not disclose data or corrupt attacker-inaccessible objects.

## 3. Reachability analysis

A remote host that can connect to the NVMe/TCP target can potentially trigger the leak by repeatedly opening and closing connections during the queue allocation error path, for example around an `-ENOTCONN` failure. No local account on the victim is required once the target listener is reachable.

This is not Internet-broad by default. NVMe/TCP targets are normally configured explicitly and deployed inside storage, cluster, or data-center networks. Containers and namespaces do not materially reduce the needed privilege on the victim because the trigger is network-side, but exposure depends on whether the NVMe/TCP target is enabled and reachable from untrusted hosts.

## 4. Severity interpretation

This behaves like an actionable Moderate resource-exhaustion issue rather than an Important memory-corruption vulnerability. The realistic impact is DoS through memory exhaustion after repeated failed connection attempts. Theoretical impact beyond DoS is not supported because the patch only drains a leaked page fragment cache reference and does not show stale object reuse, writable UAF, OOB access, arbitrary write, or ownership/COW bypass.

The conservative score stays at 4 because this is a leak requiring repeated triggering. The paranoid score is 5 because it is network-triggerable in configured storage deployments and sustained abuse can plausibly cause system-wide memory exhaustion.

## 5. One-sentence report phrase

A network-reachable NVMe/TCP target can leak page fragment cache references when connections fail during queue allocation, allowing repeated failed connections to cause kernel memory exhaustion and denial of service.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is a network-triggerable storage target DoS, even though the bug class is resource leak without memory corruption or privilege escalation evidence.

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

Patch: nvmet-tcp: fix page fragment cache leak in error path [ Upstream
Commit: a43a9abc1ebf663f0aa56a729106f68dd9c77da6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a43a9abc1ebf663f0aa56a729106f68dd9c77da6

Changed files:
  drivers/nvme/target/tcp.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=a43a9abc1ebf663f0aa56a729106f68dd9c77da6

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

The original Linux kernel CVE announcement for CVE-2026-74386 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74386

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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 4
  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).