[CVE-2026-99114][MODERATE REGULAR] ksmbd: initialize FileSystemControlFlags in FS_CONTROL_INFORMATION

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

CVE: CVE-2026-99114
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ksmbd: initialize FileSystemControlFlags in FS_CONTROL_INFORMATION
Commit: d8c450ad0d08980b39b08d435efa921086c8b227
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d8c450ad0d08980b39b08d435efa921086c8b227
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99114
Analysis date: Fri, 30 Oct 2026 12:00:26 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A remote SMB client can obtain four stale bytes from a dropped earlier compound response because ksmbd failed to initialize `FileSystemControlFlags`.

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

The original Linux kernel CVE announcement for CVE-2026-99114 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99114

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 REGULAR
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-2026-99114	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99114 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=3 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';*CWE-457;*CWE-200;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.3';DESCR 'ksmbd reports a 48 byte FS_CONTROL_INFORMATION response but did not initialize the four byte FileSystemControlFlags field. A standalone request does not leak because a newly allocated response buffer is zeroed. In a compound SMB request a previously generated response can be replaced by a short error response while its data remains in the shared buffer, allowing the next response to expose four bytes of that earlier data. For the CVSS the PR:N value is used for the paranoid score because a guest or anonymous SMB share may allow the required query lacking authenticated privileges, while typical authenticated deployments are better represented by PR:L. The demonstrated impact is a small remote confidentiality leak with no supported integrity or availability impact. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 3 with primitive class NONE and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	REMOTE DISK SIMPLEFIX LEAK SKIP LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3; anonymous-share reachability changes protocol privileges but adds no separate scoring signal.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Remote network reachability: an SMB client can invoke the filesystem-information query through ksmbd.
* +1 Confidentiality plausible: four uninitialized response bytes can contain remnants of a dropped earlier response in the same compound buffer.
* No separate common-path point: ksmbd exposure is deployment-dependent.
* No constrained-corruption penalty: the four-byte limit already prevents stronger disclosure scoring and does not negate the confirmed leak.
* No OOB write, UAF, memory corruption, authorization bypass, integrity impact, crash, or availability impact is shown.
* No Class A disclosure: the patch establishes only a four-byte stale-response disclosure, not arbitrary kernel memory reading, credentials, or a named sensitive resource.
* B5-R and B3-PENDING do not apply; there is neither a retry-accumulated write nor a shared-backing write.

3. Reachability analysis

A remote SMB client can issue the relevant compound request. Typical deployments may require an ordinary authenticated SMB account, while guest shares could permit anonymous access. Neither path requires host UID 0, host-administrator capability, namespace capability, special hardware, or a race. Guest-share availability is not assumed for the conservative score.

4. Primitive and severity reading

The primitive is a constrained four-byte information disclosure: `FileSystemControlFlags` is included in the advertised 48-byte structure but was not initialized, allowing bytes retained from an earlier dropped compound response to be returned. This is CLASS_B due to a real but narrowly bounded confidentiality effect. No protected cross-user resource, arbitrary disclosure, or privilege escalation is demonstrated. ImportantCandidate is therefore NO, and automatic Important-to-Moderate downgrade is allowed.

5. One-sentence report phrase

A remote SMB client can obtain four stale bytes from a dropped earlier compound response because ksmbd failed to initialize `FileSystemControlFlags`.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm affected ksmbd exposure and whether anonymous or low-privilege SMB clients can submit the required compound request.

7. Call-site confidence

Call-site confidence: high

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

Patch: ksmbd: initialize FileSystemControlFlags in FS_CONTROL_INFORMATION
Commit: d8c450ad0d08980b39b08d435efa921086c8b227
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d8c450ad0d08980b39b08d435efa921086c8b227

Commit description:

smb2_get_info_filesystem() reports 48 bytes for FS_CONTROL_INFORMATION,
that is the whole of struct smb2_fs_control_info, but never assigns
FileSystemControlFlags.  Those four bytes go to the client as they are
found in the response buffer.

The buffer is zeroed on allocation, so a standalone request leaks
nothing.  A compound request can leak: the offset of the next response
is advanced by the length pinned for the previous one, so a reply that
was written into the buffer and then dropped in favour of the short
error response of smb2_set_err_rsp() stays there, and the next reply is
laid over it with only the header cleared.

ksmbd does not implement quota tracking, so report no control flags.

Fixes: e2f3448 ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Signed-off-by: Aleksandr Khromov <haa@amicon.ru>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/server/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=d8c450ad0d08980b39b08d435efa921086c8b227

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

The original Linux kernel CVE announcement for CVE-2026-99114 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99114

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:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS score: 5.3

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: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).