[CVE-2026-72492][MODERATE 7.0] ksmbd: fix use-after-free in same_client_has_lease() [ Upstream

[CVE-2026-72492][MODERATE 7.0] ksmbd: fix use-after-free in same_client_has_lease() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72492
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ksmbd: fix use-after-free in same_client_has_lease() [ Upstream
Commit: aaa3bb2bbf2ccbfea9e4e0b9dabf3afc60b50cd0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aaa3bb2bbf2ccbfea9e4e0b9dabf3afc60b50cd0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72492
Analysis date: Sun, 16 Aug 2026 04:01:13 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in ksmbd lease handling can return an `oplock_info` object without holding a reference, allowing a concurrent SMB close to free it before later use in `smb_grant_oplock()`, causing a network-reachable kernel use-after-free and likely DoS.

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

The original Linux kernel CVE announcement for CVE-2026-72492 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72492

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-2026-72492	MODERATE	CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race condition in ksmbd same_client_has_lease can return an oplock_info pointer from ci m_op_list after dropping ci m_lock without holding a reference. A concurrent SMB close can remove the old lease and drop the last reference before smb_grant_oplock uses the pointer in copy_lease or checks breaking_cnt, causing a kernel use-after-free. For the CVSS the PR:L is used because reliable triggering normally requires an SMB user or guest context with access to a share rather than only network reachability to the port. The issue is network reachable through SMB lease and close operations against a ksmbd server, but AC:H is appropriate because exploitation depends on a timing race. Impact is at least remote denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact because the stale object is reused in kernel lease handling.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-72492 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE DISK UAF SKIP  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

This should **not** be auto-closed because it is a network-reachable kernel lifetime bug in ksmbd, but the patch does not show enough exploit control to rate it as a strong Important candidate by the ActionableScore formula.

## 2. Signal breakdown

Conservative signals:

* **Remote reachable / network-triggerable: +2**
  The affected path is in ksmbd SMB server lease and oplock handling, reachable via SMB operations against an enabled ksmbd share.

* **Memory corruption, weak/indirect corruption candidate: +1**
  This is a UAF, but it is race-dependent and the patch only shows a stale `oplock_info` pointer surviving a concurrent close/free. No attacker-controlled reclaim, overwrite, callback dispatch, type confusion, or refcount takeover is shown.

* **Real lifetime corruption: +1**
  The bug is a real refcount/lifetime error. `same_client_has_lease()` returned an object from `ci->m_op_list` without taking a reference.

* **Reliable kernel crash / strong DoS: +1**
  `smb_grant_oplock()` dereferences the stale object in `copy_lease()` and when checking `breaking_cnt`, making kernel crash/DoS realistic.

* **Hard or unreliable race / special timing required: -1**
  Triggering requires winning a race between lease lookup/use and a concurrent close that drops the last reference.

Conservative total: **4**

Paranoid additional signal:

* **Enabled network service exposure: +1**
  If ksmbd is deployed as an exposed SMB server with user or guest share access, lease/open/close operations are realistic remote inputs. This makes the issue more actionable even without a proven LPE primitive.

Paranoid total: **5**

## 3. Reachability analysis

A remote SMB client can potentially trigger the bug through lease/oplock related open and close activity against a ksmbd server. In typical deployments, **SMB authentication or guest share access is required**, so this is not pure unauthenticated PR:N in the usual case. Namespaces do not materially reduce the impact because the vulnerable code runs in the host kernel server path. The path is not default-enabled on every Linux system, but it is relevant on systems that run ksmbd for SMB3 file sharing.

Call-site confidence: **high**, because the provided commit explicitly names both the returning function and the dereference site: `same_client_has_lease()` returns the stale pointer and `smb_grant_oplock()` later uses it.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is a **network-reachable kernel UAF** in a server-side filesystem protocol. Realistic demonstrated impact is strongest for **remote DoS** via kernel crash. Theoretical LPE or stronger C/I impact is possible only in a paranoid sense, because UAFs can sometimes become exploitable after object reuse, but the patch does not show attacker-controlled reclaim, write-after-free, callback control, or type confusion.

Therefore, the issue is best treated as **Actionable Moderate at minimum**, with manual review required. It is not automatically a strong Important candidate without additional evidence of controlled reuse or exploitation.

## 5. One-sentence report phrase

A race in ksmbd lease handling can return an `oplock_info` object without holding a reference, allowing a concurrent SMB close to free it before later use in `smb_grant_oplock()`, causing a network-reachable kernel use-after-free and likely DoS.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: network-reachable kernel UAF in ksmbd. The current evidence supports DoS more strongly than privilege escalation, but the bug class and server-side reachability make it unsafe to auto-close without checking object reuse and exploitability conditions.

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

Patch: ksmbd: fix use-after-free in same_client_has_lease() [ Upstream
Commit: aaa3bb2bbf2ccbfea9e4e0b9dabf3afc60b50cd0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aaa3bb2bbf2ccbfea9e4e0b9dabf3afc60b50cd0

Changed files:
  fs/ksmbd/oplock.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=aaa3bb2bbf2ccbfea9e4e0b9dabf3afc60b50cd0

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

The original Linux kernel CVE announcement for CVE-2026-72492 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72492

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:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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).