[CVE-2026-72356][MODERATE REGULAR] cifs: Fix missing credit release on failure in cifs_issue_read() [ Upstream

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

CVE: CVE-2026-72356
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: cifs: Fix missing credit release on failure in cifs_issue_read() [ Upstream
Commit: b9ee1f0347bf56d019ca28ddff090234bb45b05c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9ee1f0347bf56d019ca28ddff090234bb45b05c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72356
Analysis date: Sun, 16 Aug 2026 07:15:24 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended / Ordinary Moderate network filesystem DoS
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72356 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72356

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-2026-72356	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H';*CWE-772;**CWE-400;CWE-703;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A CIFS read failure path can leak SMB credits because cifs_issue_read did not release rdata credits before terminating the failed netfs subrequest. Repeated failures and retries can overwrite the stored credits value and gradually exhaust the credit accounting for the SMB session, which may stall further reads or other I/O and cause denial of service for the mounted share. For the CVSS the PR:N reflects that a malicious or compromised SMB server does not need privileges on the client once the share is mounted and reachable. The issue is network related through the SMB client/server protocol, but reliable triggering likely requires an existing CIFS mount, read activity, and failure conditions that exercise the retry path. Impact is availability loss only unless additional evidence shows a stronger primitive than resource accounting exhaustion.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended / Ordinary Moderate network filesystem DoS (with actual score 4)  SKIP CVE-2026-72356 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 69c3c023af25edb5433a2db824d3e7cc328f0183 YES  NO NO unknown 	MAYBE	DISK SIMPLEFIX SERVERTOCLIENT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

1. ActionableScore
* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended / Ordinary Moderate network filesystem DoS**::

2. Signal breakdown
* Remote reachable / network-triggerable: +2. A malicious or compromised SMB server can plausibly influence the CIFS client failure path once the share is mounted and reads are issued.
* Availability impact realistic: +1. Leaked SMB credits can exhaust session credit accounting and stall reads or other I/O on the mounted share.
* Important filesystem/storage path: +1 in the paranoid score. CIFS is a network filesystem data path, but the bug affects credit accounting rather than metadata integrity or page-cache ownership.
* No memory corruption: +0. The patch fixes a missing credit release, not UAF, OOB, double-free, arbitrary write, or object lifetime corruption.
* No privilege escalation signal: +0. The supported impact is resource exhaustion / DoS only.
* No confidentiality or integrity impact: +0. No read disclosure, unauthorized write, or permission bypass is shown.

3. Reachability analysis
The most realistic attacker is a malicious or compromised SMB server, or possibly an attacker able to disrupt SMB responses in a way that repeatedly drives the read failure and retry path. The client must already have an active CIFS mount and must issue reads that enter cifs_issue_read(). No local privileges on the client are needed by a malicious server after the mount exists, but practical exploitation depends on mount configuration, read activity, and repeatable failure conditions. Namespaces do not materially improve reachability unless they allow untrusted users to create CIFS mounts.

4. Severity interpretation
This behaves like an ordinary to borderline Moderate resource exhaustion issue, not an Important memory corruption vulnerability. The theoretical worst case is persistent or repeated I/O stall on the affected SMB session or mounted share. There is no evidence of kernel memory corruption, privilege escalation, or cross-file data integrity impact.

5. One-sentence report phrase
A CIFS read failure path can leak SMB credits when cifs_issue_read() terminates a failed netfs subrequest without releasing rdata credits, allowing repeated failures from a malicious or faulty SMB server to exhaust session credits and cause client-side I/O denial of service.

6. Manual review recommendation
MANUAL CHECK REQUIRED.
Reason: the bug is network-filesystem reachable from a malicious or compromised SMB server and can cause practical availability impact, even though the patch supports only resource exhaustion and not memory corruption or privilege escalation.

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

Patch: cifs: Fix missing credit release on failure in cifs_issue_read() [ Upstream
Commit: b9ee1f0347bf56d019ca28ddff090234bb45b05c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9ee1f0347bf56d019ca28ddff090234bb45b05c

Changed files:
  fs/smb/client/file.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=b9ee1f0347bf56d019ca28ddff090234bb45b05c

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

The original Linux kernel CVE announcement for CVE-2026-72356 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72356

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:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:R/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: 3
  Paranoid ActionableScore: 4

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).