[CVE-2026-72363][MODERATE REGULAR] netfs: Fix folio state after ENOMEM whilst under writeback iteration [ Upstream

[CVE-2026-72363][MODERATE REGULAR] netfs: Fix folio state after ENOMEM whilst under writeback iteration [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72363
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfs: Fix folio state after ENOMEM whilst under writeback iteration [ Upstream
Commit: a9b89752c2726e88ea67994fb97a0316b24d30b7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a9b89752c2726e88ea67994fb97a0316b24d30b7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72363
Analysis date: Sun, 16 Aug 2026 09:09:14 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline ordinary Moderate / not Important
Manual review required: YES

Summary:
An ENOMEM error in netfs writeback could leave the current folio not redirtied and not unlocked before writeback iteration terminates, causing local writeback stalls or limited dirty-data retry inconsistency under memory pressure.

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

The original Linux kernel CVE announcement for CVE-2026-72363 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72363

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 REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72363	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:N/I:L/A:H';CWE-703;CWE-755;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'An ENOMEM error during netfs writeback iteration can leave the current folio in an incorrect writeback state if it is not redirtied and unlocked before the final writeback_iter() step. This can cause a local denial of service through a stalled or blocked writeback path and may also cause limited integrity impact if dirty data is not preserved for later writeback. For the CVSS the PR:L value is used because a local user or local process with write access to the affected netfs backed file is needed for practical triggering, while mounting or configuring the filesystem may require higher privileges. The issue is not directly network reachable even if the backing filesystem uses a network protocol, because the vulnerable path is local writeback error handling. Impact is mainly availability loss, with limited integrity risk in the paranoid score due to the missing redirty operation.';NO MANUAL CHECK; ,and ActionableScore result is Borderline ordinary Moderate / not Important (with actual score 3)  SKIP CVE-2026-72363 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 06fa229ceb36898e68022b5654c017d2c6582d7d YES  NO NO unknown 	MAYBE	REMOTE DISK NOMEMCHK SIMPLEFIX LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline ordinary Moderate / not Important**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user or process with write access to a netfs-backed file can reach writeback paths, though reliable ENOMEM timing is not trivial.
* Availability impact realistic: +1. A folio left locked or in the wrong writeback state can plausibly stall writeback or block filesystem I/O.
* Important filesystem/storage path: +1. The bug is in netfs writeback/page-cache handling.
* Hard or unreliable condition: -1. Triggering requires ENOMEM at a specific point during writeback iteration.

Paranoid additional signal:

* Integrity impact plausible: +1. Missing `folio_redirty_for_writepage()` may mean dirty data is not properly preserved for retry after ENOMEM, so limited writeback integrity risk is defensible.

Not awarded:

* No memory corruption signal. The patch does not show UAF, OOB access, double free, stale pointer reuse, arbitrary write, or type confusion.
* No privilege escalation signal. There is no supported LPE primitive.
* No remote reachability. Network-backed storage does not make this AV:N because the vulnerable operation is local writeback error handling.
* No Dirty-Pipe-like or CoW ownership bypass. The patch does not indicate unauthorized cross-file or shared-page modification.

## 3. Reachability analysis

A local process that can write to an affected netfs-backed file may reach this path when writeback occurs and `netfs_write_folio()` returns `-ENOMEM`. Mounting or configuring the netfs filesystem may require privileges, but triggering writeback on an already mounted filesystem can be possible for ordinary users with file write permissions.

Namespaces or containers do not materially improve reachability unless the container has access to a mounted affected filesystem. The path is not directly packet-triggered and is not exposed as a remote protocol parser. Realistic exploitation requires local filesystem activity plus memory pressure or allocation failure at the relevant writeback point, making the trigger less reliable.

Call-site confidence: high, because the changed code is directly inside the `netfs_writepages()` writeback iteration loop.

## 4. Severity interpretation

This behaves like an ordinary Moderate storage/writeback robustness issue, with a paranoid bump for possible limited data-integrity effects. It does not look like an Important-class kernel vulnerability because there is no demonstrated memory corruption, security-boundary bypass, page-cache ownership violation, or privilege-escalation primitive.

Theoretical impact is mainly local DoS through stalled writeback or locked folio state. Realistic exploitation evidence for anything beyond availability impact is weak.

## 5. One-sentence report phrase

An ENOMEM error in netfs writeback could leave the current folio not redirtied and not unlocked before writeback iteration terminates, causing local writeback stalls or limited dirty-data retry inconsistency under memory pressure.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.

Reason: no memory corruption, no network trigger, no LPE primitive, and no clear cross-boundary storage ownership violation are supported by the patch.

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

Patch: netfs: Fix folio state after ENOMEM whilst under writeback iteration [ Upstream
Commit: a9b89752c2726e88ea67994fb97a0316b24d30b7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a9b89752c2726e88ea67994fb97a0316b24d30b7

Changed files:
  fs/netfs/write_issue.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=a9b89752c2726e88ea67994fb97a0316b24d30b7

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

The original Linux kernel CVE announcement for CVE-2026-72363 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72363

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:N/I:L/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: 2
  Paranoid ActionableScore: 3

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 REGULAR

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).