[CVE-2026-72382][MODERATE 7.0] ksmbd: reject undersized DACLs before parsing ACEs [ Upstream

[CVE-2026-72382][MODERATE 7.0] ksmbd: reject undersized DACLs before parsing ACEs [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72382
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ksmbd: reject undersized DACLs before parsing ACEs [ Upstream
Commit: 16fb65ec15fe7c90f50a2115854bfd9a032d4023
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=16fb65ec15fe7c90f50a2115854bfd9a032d4023
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72382
Analysis date: Sat, 15 Aug 2026 19:38:28 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An integer underflow in ksmbd DACL parsing allows an authenticated remote SMB client to bypass ACE count validation and force large temporary ACL allocations, causing a denial of service risk on exposed ksmbd servers.

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

The original Linux kernel CVE announcement for CVE-2026-72382 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72382

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-72382	MODERATE	CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-191;*CWE-20;**CWE-400;CWE-770;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.5';DESCR 'An integer underflow in the ksmbd DACL parser can occur when a remote SMB client supplies a DACL size smaller than the struct smb_acl header. The unsigned subtraction in the ACE count validation can turn the remaining DACL length into a very large value, allowing an attacker controlled num_aces value to bypass the intended guard and drive large temporary ACL state and pointer array allocations. For the CVSS the PR:L is used because triggering SMB2_SET_INFO for security information normally requires an authenticated SMB session and sufficient access to the target object, although practical exposure depends on share and guest access configuration. The issue is network reachable when ksmbd is exposed to untrusted SMB clients. Impact is primarily denial of service through memory pressure or allocation failure on the server. No direct UAF or OOB write primitive is evident from the patch, so confidentiality and integrity are not raised in the base score.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-72382 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE OOB DANGER DISK SKIP  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	-	-	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

Conservative signals:

* Remote reachable / network-triggerable: +2
  The affected path is reachable through SMB2_SET_INFO with InfoType=SMB2_O_INFO_SECURITY against a ksmbd server.
* Reliable kernel crash / strong DoS: +1
  The malformed DACL can bypass the intended ACE count guard and force large temporary ACL state and pointer-array allocations.
* Availability impact realistic: +1
  Repeated malformed requests can plausibly create memory pressure or allocation failure on the server.

Conservative total: 4

Paranoid additional signal:

* Broad network service parser exposure: +1
  ksmbd is not always enabled by default, but when deployed it is a network-facing SMB server parser handling attacker-controlled security descriptors.

Paranoid total: 5

Not awarded:

* Generic memory corruption: +0
  The patch shows integer underflow leading to excessive allocation, not UAF, OOB write, double free, type confusion, or arbitrary write.
* Privilege escalation plausible: +0
  No concrete LPE or memory corruption primitive is supported by the patch.
* Confidentiality / integrity impact: +0
  The demonstrated effect is allocation pressure / DoS, not disclosure or unauthorized modification.

## 3. Reachability analysis

A remote SMB client can trigger the vulnerable path by sending a malformed security descriptor through SMB2_SET_INFO. In typical deployments this requires an authenticated SMB session and sufficient access to set security information on an object, so this is not PR:N in practical CVSS terms. Guest or permissive share configurations may reduce the practical barrier.

Namespaces are not the main factor here. The relevant exposure is whether ksmbd is enabled and reachable from untrusted clients. ksmbd is not a universal default service, but SMB servers are commonly deployed in enterprise and appliance environments. Realistic exploitation is mainly resource exhaustion against an exposed ksmbd instance rather than code execution.

Call-site confidence: high. The commit message provides the full call path into parse_dacl and describes the allocation consequence.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary low-priority Moderate. The issue is network reachable and attacker-controlled size/count fields can drive large kernel allocations. However, the patch does not demonstrate memory corruption, stale object reuse, OOB write, or privilege escalation. The realistic impact is DoS through memory pressure or allocation failure. The paranoid score is elevated to 5 because network-facing parser bugs in SMB server code should not be auto-closed without review, even when the visible primitive is resource exhaustion.

## 5. One-sentence report phrase

An integer underflow in ksmbd DACL parsing allows an authenticated remote SMB client to bypass ACE count validation and force large temporary ACL allocations, causing a denial of service risk on exposed ksmbd servers.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable SMB server parser bug with attacker-controlled length and count fields. Current evidence supports DoS rather than memory corruption, but the exposure and parser context make it inappropriate for automatic closure without human review.

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

Patch: ksmbd: reject undersized DACLs before parsing ACEs [ Upstream
Commit: 16fb65ec15fe7c90f50a2115854bfd9a032d4023
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=16fb65ec15fe7c90f50a2115854bfd9a032d4023

Changed files:
  fs/smb/server/smbacl.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=16fb65ec15fe7c90f50a2115854bfd9a032d4023

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

The original Linux kernel CVE announcement for CVE-2026-72382 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72382

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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).