[CVE-2026-64069][MODERATE 7.0] netfs: Fix cancellation of a DIO and single read subrequests [ Upstream

[CVE-2026-64069][MODERATE 7.0] netfs: Fix cancellation of a DIO and single read subrequests [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64069
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfs: Fix cancellation of a DIO and single read subrequests [ Upstream
Commit: 5366199be46fb53de62861721d34ba816e7e440e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5366199be46fb53de62861721d34ba816e7e440e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64069
Analysis date: Sun, 19 Jul 2026 21:18:48 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A netfs read cancellation lifetime bug can leave a failed queued subrequest visible to the collector while references are mishandled, creating a plausible stale-list or UAF-style condition with local DoS impact and requiring manual review for escalation risk.

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

The original Linux kernel CVE announcement for CVE-2026-64069 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64069

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
======================================================================

CVE-2026-64069	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:H/I:H/A:H';*CWE-416;CWE-362;CWE-911;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A lifetime and cancellation bug in the netfs read path can occur when preparation of a DIO or single read subrequest fails after the subrequest has been linked into the stream subrequests list. The failed subrequest may still be visible to the collector, while the old error path could drop references or abandon the object without marking it failed and completing it through the normal termination path. This creates a reference lifetime race and a plausible use after free or stale list traversal condition, with the most direct impact being a local kernel crash or I/O hang. For the CVSS the PR:L is used because a local user or process that can read from an affected mounted netfs filesystem may be able to reach the path, although reliable triggering also depends on preparation failure conditions. The issue is not directly network reachable by arbitrary packets. Impact is at least denial of service, and for the paranoid score it may allow broader confidentiality or integrity impact due to the use after free candidate and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-64069 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: e2d46f2ec332533816417b60933954173f602121 YES  NO NO unknown 	MAYBE	REMOTE READ LOCK DISK NOMEMCHK LINUS KPANIC 	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process that can read from an affected mounted netfs-backed filesystem may reach the read path.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch describes a queued subrequest that may still be visible to the collector while the old error path drops or abandons references. This is a plausible stale-list or UAF-style lifetime issue, but no controlled reclaim, write-after-free, callback control, or object replacement is shown.

* Real lifetime corruption: +1
  The bug is explicitly about subrequest ownership, reference handling, cancellation, and handoff to the collector.

* Reliable kernel crash / strong DoS: +1
  Incorrect cancellation of visible subrequests can plausibly cause kernel crash, hang, or read-collector state corruption.

* Important filesystem/storage path: +1
  This is in the netfs read path, including DIO and single-read handling. It affects filesystem I/O request lifetime and completion handling.

* Hard or special triggering conditions: -1
  Triggering requires a preparation failure after specific subrequest queuing or dispatch ordering, so it is not a trivial read-only crash path.

* Race-UAF downgrade / cap applied
  No evidence is provided for attacker-controlled reclaim, type confusion, writable stale object access, callback dispatch, or refcount takeover. Conservative score is capped at 4 and paranoid score at 5.

## 3. Reachability analysis

The likely attacker is a local user or local process able to perform reads against an affected mounted netfs filesystem. The issue is not directly network-triggerable by arbitrary packets, although the filesystem backend may involve network storage. Namespaces or containers may matter if an untrusted workload is given access to the mounted filesystem, but the bug is still best modeled as local PR:L rather than remote. The path is not universally default-exposed because it depends on netfs users and on DIO or single-read preparation failure conditions.

Call-site confidence: high. The provided patch includes the affected buffered, direct, single-read, and collector paths.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it involves real kernel object lifetime and collector visibility, not just an error-code cleanup bug. Realistic demonstrated impact is mainly local DoS through crash, hang, or corrupted read completion state. The paranoid interpretation treats it as Actionable Moderate because the object lifetime pattern is a plausible UAF candidate, but current evidence does not justify Important-class scoring without controlled reclaim, write primitive, callback control, or a demonstrated LPE path.

## 5. One-sentence report phrase

A netfs read cancellation lifetime bug can leave a failed queued subrequest visible to the collector while references are mishandled, creating a plausible stale-list or UAF-style condition with local DoS impact and requiring manual review for escalation risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because the patch fixes a reference-lifetime and queued-object cancellation problem where the collector may observe an object after the old path mishandled cancellation. The realistic impact is likely DoS, but the lifetime pattern is sufficient for manual review.

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

Patch: netfs: Fix cancellation of a DIO and single read subrequests [ Upstream
Commit: 5366199be46fb53de62861721d34ba816e7e440e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5366199be46fb53de62861721d34ba816e7e440e

Changed files:
  fs/netfs/buffered_read.c
  fs/netfs/direct_read.c
  fs/netfs/internal.h
  fs/netfs/read_collect.c
  fs/netfs/read_single.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=5366199be46fb53de62861721d34ba816e7e440e

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

The original Linux kernel CVE announcement for CVE-2026-64069 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64069

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:L/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:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 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: YES
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).