[CVE-2026-46195][IMPORTANT] smb: client: validate dacloffset before building DACL pointers

[CVE-2026-46195][IMPORTANT] smb: client: validate dacloffset before building DACL pointers

[AL-KERNEL]

CVE: CVE-2026-46195
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: smb: client: validate dacloffset before building DACL pointers
Commit: ba7f71b6161c0943dafc367565e5843d16b7d505
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ba7f71b6161c0943dafc367565e5843d16b7d505
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46195
Analysis date: Thu, 28 May 2026 09:53:23 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious SMB server can craft a DACL offset that wraps pointer arithmetic on 32-bit clients, allowing SMB ACL parsing or rewrite paths to dereference out-of-bounds kernel memory and potentially crash or disclose data.

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

The original Linux kernel CVE announcement for CVE-2026-46195 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46195

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-2026-46195	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:L/A:H';CWE-125;CWE-190;*CWE-20;*CWE-200;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:H';BEST CVSS score: '8.3';DESCR 'A malicious SMB server can return a crafted DACL offset in a security descriptor so that 32-bit clients compute a wrapped DACL pointer before validating that the DACL header fits in the descriptor. The wrapped pointer can pass later pointer based checks and be dereferenced in ACL parse or chmod chown rewrite paths, causing an out-of-bounds kernel read and possible client crash. For the CVSS the PR:N is used because the attacker only needs to control the SMB server response, while the victim must connect to the server or perform an ACL related operation. The issue is network reachable from a malicious or compromised SMB server, but it is not a generic Internet packet path. Impact is at least denial of service and possible kernel information disclosure, especially if bogus DACL data is copied into an ACL rewrite request.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	OOB DISK INIT SERVERTOCLIENT KPANIC  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* 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 return a crafted security descriptor to a client.
* Weak/indirect memory corruption candidate: +1. The primitive is a server-controlled pointer wrap and invalid kernel pointer interpretation on 32-bit builds.
* Reliable kernel crash / strong DoS: +1. Dereferencing the wrapped DACL pointer can crash the client kernel.
* Confidentiality impact plausible: +1. The invalid DACL read may expose kernel memory through ACL parsing or rewrite behavior.
* Availability impact realistic: +1. Client crash is plausible.
* Common networking / storage path: +1. SMB/CIFS client is a common network filesystem path.
* Constrained primitive / 32-bit-only pointer wrap: -1. The strongest supported primitive is OOB read on 32-bit clients, not an arbitrary write.

Paranoid additional signal:

* Integrity impact plausible: +1. In chmod/chown ACL rewrite paths, bogus DACL fields may influence the rebuilt security descriptor or outbound ACL update, though no direct arbitrary write primitive is shown.

## 3. Reachability analysis

The attacker controls the SMB server or compromises a server that the victim client mounts or accesses. The victim must connect to that server and perform an operation that parses or rewrites security descriptors, such as ACL handling, chmod, or chown.

This is not a raw unauthenticated Internet packet path against a listening client. It is still network-reachable in the client-server trust model because the attacker-controlled server supplies the malformed descriptor. The most important limitation is architecture: the pointer wrap described is specific to 32-bit builds.

Namespaces and containers matter if CIFS mounts are performed in containers or delegated mount environments, but the primary risk is to the kernel SMB client on the host performing the mount.

## 4. Severity interpretation

This is at least an actionable Moderate and a strong Important candidate for affected 32-bit clients. The realistic impact is kernel OOB read and client crash. The higher-risk interpretation is kernel information disclosure and limited ACL integrity influence in rewrite paths.

This should not be treated as a generic LPE or arbitrary kernel write. The patch supports OOB read and pointer-wrap bounds bypass, not a proven write primitive.

## 5. One-sentence report phrase

A malicious SMB server can craft a DACL offset that wraps pointer arithmetic on 32-bit clients, allowing SMB ACL parsing or rewrite paths to dereference out-of-bounds kernel memory and potentially crash or disclose data.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Network-supplied data controls the invalid pointer calculation in a kernel filesystem client, and the impact depends on 32-bit deployment, ACL rewrite paths, and whether OOB reads can be reflected or otherwise exposed.

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

Patch: smb: client: validate dacloffset before building DACL pointers
Commit: ba7f71b6161c0943dafc367565e5843d16b7d505
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ba7f71b6161c0943dafc367565e5843d16b7d505

Commit description:

parse_sec_desc(), build_sec_desc(), and the chown path in
id_mode_to_cifs_acl() all add the server-supplied dacloffset to pntsd
before proving a DACL header fits inside the returned security
descriptor.

On 32-bit builds a malicious server can return dacloffset near
U32_MAX, wrap the derived DACL pointer below end_of_acl, and then slip
past the later pointer-based bounds checks. build_sec_desc() and
id_mode_to_cifs_acl() can then dereference DACL fields from the wrapped
pointer in the chmod/chown rewrite paths.

Validate dacloffset numerically before building any DACL pointer and
reuse the same helper at the three DACL entry points.

Fixes: bc3e9dd ("cifs: Change SIDs in ACEs while transferring file ownership.")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/cifsacl.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=ba7f71b6161c0943dafc367565e5843d16b7d505

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

The original Linux kernel CVE announcement for CVE-2026-46195 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46195

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:H/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:H
  The Best / paranoid CVSS score: 8.3

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: 7

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).