[CVE-2026-72376][LOW] afs: Fix misplaced inc of net->cells_outstanding [ Upstream

[CVE-2026-72376][LOW] afs: Fix misplaced inc of net->cells_outstanding [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72376
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: afs: Fix misplaced inc of net->cells_outstanding [ Upstream
Commit: 6e310f818abcef947a06584158b9e6c6cd0c98d3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e310f818abcef947a06584158b9e6c6cd0c98d3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72376
Analysis date: Sat, 15 Aug 2026 03:57:47 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
AFS cell allocation could leave `net->cells_outstanding` permanently overcounted when `idr_alloc_cyclic()` fails, potentially causing resource-accounting based cleanup or availability issues without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-72376 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72376

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: LOW
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
======================================================================

CVE-2026-72376	LOW	CHECK WITH IMPACT FROM ORIG NN NONE	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:N/A:H';CWE-911;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'AFS cell allocation increments net cells_outstanding before idr_alloc_cyclic() is known to have succeeded. If idr_alloc_cyclic() fails, the error path can leave the outstanding cell counter permanently overcounted, which may block later cleanup or cause resource accounting based denial of service. This is a local control plane issue and is not directly network reachable, even though AFS itself is a network filesystem. For the CVSS the PR:L is used for the paranoid score because some deployments may allow a local unprivileged user to trigger AFS automount or dynamic root cell creation, while the base score assumes administrator controlled AFS setup. Attack complexity remains high because reliable triggering depends on hitting the allocation failure path. Impact is availability only, with no concrete evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	DISK SIMPLEFIX SKIP IMPROVEONLY LINUS 	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Requires admin/root/CAP_* in typical deployments: -2. AFS cell setup or mount configuration is normally administrator controlled.
* Hard or unreliable trigger condition: -1. The bug requires `idr_alloc_cyclic()` failure after partial cell allocation.
* Availability impact realistic: +1. A stale `cells_outstanding` overcount may block cleanup or create resource-accounting based DoS.
* No memory corruption signal. The patch only moves an accounting increment after successful ID allocation.
* No LPE signal. No UAF, double free, stale pointer reuse, controlled overwrite, or privilege boundary bypass is shown.

Paranoid adjustment:

* Local unprivileged trigger: +1. In some deployments, a local user may indirectly trigger AFS automount or dynamic cell creation.
* Availability impact realistic: +1.
* Hard allocation failure path: -1.
* Result: 1.

Call-site confidence: medium. The changed function is visible, but broader cleanup users of `cells_outstanding` are not shown in the provided patch.

## 3. Reachability analysis

The affected path is local AFS cell allocation. It is not directly network-triggerable, despite AFS being a network filesystem. Typical exploitation requires the ability to cause AFS cell creation plus an `idr_alloc_cyclic()` failure path. In normal deployments this is likely administrator-controlled, but paranoid triage can consider local unprivileged reachability if automount or dynroot behavior is exposed to users. Containers and namespaces may matter only if they can trigger AFS mounts or automounts, which is not generally default.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource-accounting bug, not an Important-class vulnerability. The realistic impact is availability only through stale accounting and possible cleanup blockage. There is no supported memory corruption primitive, no information disclosure, no integrity impact, and no plausible privilege escalation path from the patch context.

## 5. One-sentence report phrase

AFS cell allocation could leave `net->cells_outstanding` permanently overcounted when `idr_alloc_cyclic()` fails, potentially causing resource-accounting based cleanup or availability issues without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.

Reason: this is a resource-accounting/error-path bug with no concrete memory corruption, no network reachability, no privilege escalation primitive, and only low-confidence availability impact.

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

Patch: afs: Fix misplaced inc of net->cells_outstanding [ Upstream
Commit: 6e310f818abcef947a06584158b9e6c6cd0c98d3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e310f818abcef947a06584158b9e6c6cd0c98d3

Changed files:
  fs/afs/cell.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=6e310f818abcef947a06584158b9e6c6cd0c98d3

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

The original Linux kernel CVE announcement for CVE-2026-72376 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72376

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).