[CVE-2026-64382][IMPORTANT] smb: client: fix double-free in SMB2_open() replay

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

CVE: CVE-2026-64382
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: smb: client: fix double-free in SMB2_open() replay
Commit: 02bc2896bdc3e29362d6e40d404006944a159c25
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02bc2896bdc3e29362d6e40d404006944a159c25
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64382
Analysis date: Sat, 25 Jul 2026 14:33:58 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A stale response-buffer state in the SMB2_open() replay path can cause a double-free when a malicious SMB server returns a replayable error and the next replay attempt fails before initializing a new response, leading to kernel memory corruption and at least a remote DoS risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64382 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64382

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: IMPORTANT
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-2026-64382	IMPORTANT	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:N/S:U/C:H/I:H/A:H';CWE-415;*CWE-672;*CWE-416;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A double-free can occur in the SMB client SMB2_open() replay path because response buffer bookkeeping from a previous response-bearing attempt may remain valid after that buffer was already freed. A malicious or compromised SMB server can influence the client by returning a replayable error and causing the next replay attempt to fail before a new response buffer is initialized. For the CVSS the PR:N is used because the attacker does not need local privileges on the victim system when acting as the SMB server or controlling the network path. The base score uses UI:R because a victim client normally needs to connect to or access the SMB share. The paranoid score uses UI:N for already mounted or automatically accessed SMB shares where the server can trigger the condition without new user action. Impact is at least denial of service via kernel crash. In the worst case, the double-free memory corruption may allow confidentiality or integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)	YES	DANGER DISK UAF SERVERTOCLIENT KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. A malicious or compromised SMB server can influence the SMB client replay path after the client connects or has an active mount.
* Memory corruption, strong corruption primitive: +2. The commit explicitly describes a double-free of a response buffer.
* Real lifetime corruption: +1. The bug is stale response-buffer bookkeeping leading to freeing an already freed buffer.
* Reliable kernel crash / strong DoS: +1. Double-free in kernel client code is a realistic crash condition.
* Important filesystem/storage path: +1. SMB client is a network filesystem path used for file access.
* Hard or unreliable sequence required: -1. Triggering requires a replayable error and SMB2_open_init() failure before the next send.

Paranoid additional signals:

* Weak LPE concern: +1. Kernel heap double-free can be a possible exploitation primitive, although no controlled reclaim or overwrite is shown in the patch.
* Broad/common subsystem exposure: +1. SMB/CIFS clients are commonly deployed in enterprise and storage environments.

Not counted conservatively:

* Confidentiality and integrity impact are not counted in the lower score because the patch does not show a concrete info leak, arbitrary write, controlled reclaim, or object replacement primitive.
* Availability is not double-counted beyond the strong DoS signal.

## 3. Reachability analysis

The realistic attacker is a malicious SMB server, compromised SMB server, or network attacker able to influence the SMB session. A victim client normally must connect to or already have mounted the SMB share, so practical exposure depends on SMB client use and automount or application access patterns. No local privileges on the victim are required for the server-side attacker model. Containers and namespaces do not materially reduce the remote server influence if the host kernel SMB client performs the mount or file access. The path is not universally default-enabled, but SMB client usage is common enough that this should not be treated as a rare subsystem.

Call-site confidence: medium. The patch context clearly shows SMB2_open() replay cleanup state, but the full cleanup/free call path is not included in the provided diff.

## 4. Severity interpretation

This is stronger than ordinary Moderate because it is network-influenced kernel memory corruption in a filesystem client. The conservative interpretation is Actionable Moderate because the demonstrated impact is primarily a kernel crash and the trigger sequence is specific. The paranoid interpretation is Strong Important candidate because double-free bugs can sometimes become exploitable beyond DoS, especially in kernel heap contexts, even though this patch does not prove a reliable privilege escalation primitive.

## 5. One-sentence report phrase

A stale response-buffer state in the SMB2_open() replay path can cause a double-free when a malicious SMB server returns a replayable error and the next replay attempt fails before initializing a new response, leading to kernel memory corruption and at least a remote DoS risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is network-influenced kernel double-free memory corruption in the SMB client. Even though the reliable demonstrated impact is DoS, the bug class and remote server control make it unsuitable for auto-closure.

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UPSTREAM PATCH SUMMARY
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Patch: smb: client: fix double-free in SMB2_open() replay
Commit: 02bc2896bdc3e29362d6e40d404006944a159c25
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02bc2896bdc3e29362d6e40d404006944a159c25

Commit description:

A response-bearing attempt can return a replayable error and free its
response buffer. If SMB2_open_init() fails before the next send, cleanup
retains the previous buffer type and frees that response again.

Reset response bookkeeping before each attempt to prevent the stale free.

Fixes: 4f1fffa ("cifs: commands that are retried should have replay flag set")
Cc: stable@vger.kernel.org
Signed-off-by: Henrique Carvalho <henrique.carvalho@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/smb2pdu.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=02bc2896bdc3e29362d6e40d404006944a159c25

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

The original Linux kernel CVE announcement for CVE-2026-64382 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64382

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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: 6
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).