[CVE-2026-72310][MODERATE 7.0] smb: client: fix overflow in passthrough ioctl bounds check [ Upstream

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

CVE: CVE-2026-72310
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: fix overflow in passthrough ioctl bounds check [ Upstream
Commit: 175357ee0c596cb82054650dfa32fda51ad35aaa
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=175357ee0c596cb82054650dfa32fda51ad35aaa
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72310
Analysis date: Sat, 15 Aug 2026 05:28:26 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An integer overflow in the SMB client PASSTHRU_FSCTL response bounds check can let a malicious SMB server influence an out-of-bounds kernel read that is copied to userspace, causing possible kernel memory disclosure and potential DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72310 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72310

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-2026-72310	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H';CWE-190;CWE-125;*CWE-200;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L';BEST CVSS score: '8.1';DESCR 'An integer overflow in the SMB client PASSTHRU_FSCTL response bounds check can allow OutputOffset plus length to wrap before it is compared with the response buffer size. A malicious SMB server can craft a large OutputOffset and a small OutputCount so the wrapped bounds check succeeds and copy_to_user reads from io_rsp plus OutputOffset outside the received response buffer. For the CVSS the PR:N is used for the paranoid network model because the attacker can be a malicious SMB server and does not need an account on the client, although practical triggering may require the client to mount the share and issue the passthrough ioctl. The issue is network influenced through SMB server responses and may disclose kernel memory to userspace or cause denial of service. Impact is primarily information disclosure with possible availability impact, not a proven privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	READ OOB DANGER DISK SIMPLEFIX ERRORPATH IMPROVEONLY SERVERTOCLIENT KPANIC  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative score signals:

* Local unprivileged trigger: +1
  A local process with access to the mounted SMB filesystem and the relevant passthrough ioctl path can participate in triggering the vulnerable copy path.

* Confidentiality impact plausible: +1
  The bug is an out-of-bounds kernel read that is copied to userspace via `copy_to_user()`.

* Important filesystem/storage path: +1
  The affected code is in the SMB/CIFS client filesystem path.

* Broad/common subsystem exposure: +1
  SMB/CIFS is a commonly deployed network filesystem client, although the vulnerable path requires an SMB mount and a specific ioctl flow.

Paranoid score changes:

* Remote reachable / network-triggerable: +2
  A malicious SMB server controls `OutputOffset` and `OutputCount` in the response and can influence the vulnerable bounds check. This is network-influenced, but practical triggering still requires a client-side operation against that server.

* Availability impact realistic: +1
  The out-of-bounds read may fault or crash depending on the resulting address, although the strongest demonstrated primitive is information disclosure.

Not awarded:

* Generic memory corruption: +0
  This is an OOB read, not OOB write, UAF, double-free, heap overwrite, or arbitrary write.

* Privilege escalation plausible: +0
  No write primitive, controlled object replacement, type confusion, refcount takeover, or callback control is shown.

* Dirty-Pipe-like / page-cache corruption: +0
  The patch does not show writes into shared file-backed pages or a CoW ownership bypass.

## 3. Reachability analysis

A malicious SMB server can craft a response where `OutputOffset + input_buffer_length` wraps before comparison with `rsp_iov[1].iov_len`. The later `copy_to_user()` reads from `io_rsp + OutputOffset`, outside the received SMB response buffer.

Realistic exploitation requires the client to connect to or mount the malicious SMB server and issue the relevant PASSTHRU_FSCTL ioctl path. In the local-attacker model, a local user with access to the SMB mount may receive leaked kernel memory. In the malicious-server model, the server can trigger the bad response, but direct confidentiality benefit to the remote server is less clear unless the local caller is attacker-controlled or the result is otherwise exposed.

Namespaces do not substantially reduce the concern if an untrusted user can access an existing SMB mount and invoke the ioctl. Creating SMB mounts is commonly privileged, but using an already mounted share may be available to ordinary users depending on mount options and policy.

Call-site confidence: high. The patch and commit message explicitly describe the overflowed bounds check and the subsequent `copy_to_user()` OOB read.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a network-influenced kernel out-of-bounds read in a filesystem client and can plausibly disclose kernel memory to userspace. It is not a strong Important by default because the patch does not show memory corruption, arbitrary write, page-cache corruption, or a direct privilege-escalation primitive.

The conservative interpretation is a local information disclosure through an SMB-mounted filesystem. The paranoid interpretation treats the malicious SMB server as the primary influence source and includes possible DoS, making it an Actionable Moderate that should not be auto-closed.

## 5. One-sentence report phrase

An integer overflow in the SMB client PASSTHRU_FSCTL response bounds check can let a malicious SMB server influence an out-of-bounds kernel read that is copied to userspace, causing possible kernel memory disclosure and potential DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a network-influenced kernel OOB read with plausible confidentiality impact, and the exact severity depends on whether untrusted users can access the affected ioctl path and whether the leaked data is observable by an attacker-controlled process.

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

Patch: smb: client: fix overflow in passthrough ioctl bounds check [ Upstream
Commit: 175357ee0c596cb82054650dfa32fda51ad35aaa
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=175357ee0c596cb82054650dfa32fda51ad35aaa

Changed files:
  fs/cifs/smb2ops.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=175357ee0c596cb82054650dfa32fda51ad35aaa

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

The original Linux kernel CVE announcement for CVE-2026-72310 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72310

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:L/PR:L/UI:N/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 8.1

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: 6

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).