[CVE-2026-93794][LOW] smb/client: flush dirty data before punching a hole [ Upstream

[CVE-2026-93794][LOW] smb/client: flush dirty data before punching a hole [ Upstream

[AL-KERNEL]

CVE: CVE-2026-93794
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: smb/client: flush dirty data before punching a hole [ Upstream
Commit: 6c265aca08155e519a8f6f6071c59dff4f535f70
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c265aca08155e519a8f6f6071c59dff4f535f70
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93794
Analysis date: Thu, 24 Sep 2026 18:09:00 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93794 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93794

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-93794	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93794 CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';CWE-362;*CWE-664;CWE-693;BEST CVSS score: '3.3';DESCR 'The SMB client hole punching path can leave dirty page cache data pending while it issues a hole punch request to the SMB server. A dirty folio that overlaps the punched range can later be written back and refill the intended hole with previously buffered data. This causes inconsistent sparse file behavior and incorrect SEEK_HOLE or SEEK_DATA results for the affected file. For the CVSS the PR:L metric is used because an attacker needs local access and permission to write to and punch holes in a file on the mounted SMB share. The issue is not directly network reachable because SMB server access alone does not trigger the vulnerable client side operation on another system. Impact is limited integrity loss for data in a file that the attacker can already modify. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	DISK INIT SKIP SERVERTOCLIENT 	NO	NO	checked

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

ActionableScore=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

2. Signal breakdown

* +1 Local unprivileged trigger. A local user who already has write permission for a file on an existing SMB mount can perform buffered writes followed by hole punching on that file. Host-admin-equivalent privilege is not required for this file operation.
* +1 Filesystem and storage path. The issue affects SMB client page-cache and writeback ordering for sparse-file hole punching.

Important non-awarded signals:

* No UAF, stale post-free object use, double release, refcount mutation, OOB access, or memory corruption is established.
* No attacker-controlled kernel-memory payload, target selection, controlled reclaim, arbitrary write, or structured-object replacement is established.
* No unauthorized modification of another principals file or protected shared storage is established. The affected dirty data belongs to the same file that the triggering user must already be allowed to modify.
* No Dirty-Pipe-like shared-page or COW ownership violation is established. The patch concerns ordering between local page-cache writeback and a hole-punch request for the same SMB file.
* No remote reachability is established. An SMB server or network peer cannot trigger the vulnerable operation in a victim SMB client without a local client-side operation.
* No kernel crash, filesystem shutdown, persistent resource exhaustion, information disclosure, privilege escalation, or security-boundary bypass is established.
* No timing penalty was applied. The behavior is an ordering and writeback-consistency issue, not a narrow externally uncontrollable race.

3. Reachability analysis

The triggering actor is a local process using an already mounted SMB share and operating on a file for which it has write access and permission to issue the hole-punch operation.

The complete vulnerable sequence consists of a buffered write followed by a hole-punch request. This does not require host root, CAP_SYS_ADMIN, CAP_NET_ADMIN, or a namespace-specific capability. It does require pre-existing SMB mount setup and file-level access, but those are normal deployment and authorization prerequisites rather than host-admin-equivalent attacker privileges.

Namespace-scoped privilege is not relevant to the identified vulnerable operation. The supplied evidence does not establish a namespace capability chain, so NamespaceScopedPrivilege is UNKNOWN.

No unusual hardware, boot option, sysctl, privileged control-plane interface, or special device is required. The issue depends on SMB sparse-file support and a dirty folio spanning the punched range.

4. Primitive and severity interpretation

The exact primitive is a page-cache and writeback ordering inconsistency. A dirty folio covering the punched range can be written back after the SMB client issues the server-side zero-data operation, causing the intended sparse hole to be refilled with previously buffered data.

This is not an active-object lifetime bug and not a fixed stale-storage UAF. No object is freed and later dereferenced. No second release, put, free, or refcount operation exists.

The demonstrated consequence is incorrect sparse-file state and incorrect SEEK_HOLE or SEEK_DATA behavior for the same file. The practical impact is limited to integrity and semantic correctness of data that the triggering principal is already authorized to write.

There is no patch-supported mechanism showing that a write authorized for file A can modify independently permissioned file B, shared file-backed pages, kernel state, credentials, or filesystem metadata belonging to another principal. Therefore this is PrimitiveClass NONE rather than Class A, B, or C.

ImportantCandidate is NO because no unresolved corruption, ownership violation, authorization bypass, or exploitable lifetime primitive remains. AutoDowngradeAllowed is YES because the issue is a constrained file-consistency defect without a meaningful unresolved security primitive.

Likely operational severity is ordinary Moderate or lower. It should be fixed for sparse-file correctness, but the supplied evidence does not support treating it as an Important-class kernel-security vulnerability.

5. One-sentence report phrase

An SMB client writeback ordering flaw can refill a hole-punched range with previously buffered dirty data, causing incorrect sparse-file and SEEK_HOLE behavior for a file the local user is already authorized to modify.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a same-file page-cache consistency issue without memory corruption, cross-file ownership violation, authorization bypass, remote trigger, or privilege-escalation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: smb/client: flush dirty data before punching a hole [ Upstream
Commit: 6c265aca08155e519a8f6f6071c59dff4f535f70
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c265aca08155e519a8f6f6071c59dff4f535f70

Changed files:
  fs/smb/client/smb2ops.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=6c265aca08155e519a8f6f6071c59dff4f535f70

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

The original Linux kernel CVE announcement for CVE-2026-93794 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93794

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS score: 3.3

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).