[CVE-2026-45972][IMPORTANT] smb: client: fix potential UAF and double free in smb2_open_file() [ Upstream

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

CVE: CVE-2026-45972
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: smb: client: fix potential UAF and double free in smb2_open_file() [ Upstream
Commit: 96e53bb3ee2f354cf6b4ab07bcc56e500f8b3f74
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96e53bb3ee2f354cf6b4ab07bcc56e500f8b3f74
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45972
Analysis date: Wed, 27 May 2026 18:43:48 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
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-2026-45972 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45972

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
======================================================================

CVE-2026-45972	IMPORTANT	CHECK	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:H/A:H';*CWE-416;CWE-415;CWE-703;*CWE-664;Other CVSS 'AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '8.8';DESCR 'smb2_open_file() can free the SMB2_open error response buffer before retrying the open request, but leave err_iov and err_buftype pointing to the old freed state. A malicious or compromised SMB server can trigger the retry path by returning EACCES and then influence later error handling, causing a use after free or double free in the kernel SMB client. For the CVSS the PR:N is used because no privileges are required on the victim once the client connects to the attacker controlled SMB server, while UI:R reflects that a user or system action normally has to access the SMB share. The issue is network reachable from the server side, but it is not a generic unauthenticated packet parser against arbitrary hosts. Impact is at least denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	DISK LEAK UAF SERVERTOCLIENT  INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS	-	-	checked

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

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
* Remote/server-side reachable: +2. A malicious or compromised SMB server can influence client responses once the victim connects.
* Generic memory corruption, strong primitive: +2. The commit explicitly fixes a potential UAF and double free.
* Real lifetime corruption: +1. `err_iov` and `err_buftype` retain stale freed response-buffer state across an SMB2 open retry.
* Reliable kernel crash / strong DoS: +1. UAF or double free in the kernel SMB client can crash the system.
* Paranoid LPE / C/I concern: +1. UAF/double-free in a network filesystem client may be exploitable beyond DoS, though no controlled reclaim primitive is demonstrated.
* User interaction required: practical caveat. The victim normally must mount or access an attacker-controlled SMB share.
* Not a generic unauthenticated remote kernel parser. Exposure depends on client-initiated SMB access.

3. Reachability analysis
The vulnerable path is reached when the Linux SMB client performs `SMB2_open()` and retries after `EACCES` with `retry_without_read_attributes`. A malicious SMB server can shape responses to hit this path, but the victim must connect to or access that server or share. No local privileges are required on the victim after the connection is established. Containers may be relevant if they can trigger host SMB mounts or access kernel CIFS mounts.

4. Severity interpretation
This is a strong Important candidate in paranoid triage because it is explicit memory corruption in a network filesystem client influenced by a remote server. Conservative handling is still Actionable Moderate because user/system action is needed to access the share. The realistic minimum impact is kernel crash, while confidentiality or integrity impact is plausible from UAF/double-free but not proven by the patch alone.

5. One-sentence report phrase
A malicious SMB server can trigger an `SMB2_open()` retry path that reuses stale freed error-buffer state in the Linux SMB client, causing UAF or double-free memory corruption.

6. Manual review recommendation
MANUAL CHECK REQUIRED. The patch fixes explicit UAF/double-free in a remote-server-influenced SMB client path, making it unsuitable for automatic closure as DoS-only.

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

Patch: smb: client: fix potential UAF and double free in smb2_open_file() [ Upstream
Commit: 96e53bb3ee2f354cf6b4ab07bcc56e500f8b3f74
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96e53bb3ee2f354cf6b4ab07bcc56e500f8b3f74

Changed files:
  fs/smb/client/smb2file.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=96e53bb3ee2f354cf6b4ab07bcc56e500f8b3f74

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

The original Linux kernel CVE announcement for CVE-2026-45972 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45972

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:N/UI:R/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.8

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: NO
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).