[CVE-2026-98454][MODERATE 7.0] smb: client: fix create context out-of-bounds reads

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

CVE: CVE-2026-98454
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: fix create context out-of-bounds reads
Commit: e4c49012708c917eafd9c27054b02d0f8b30fe64
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e4c49012708c917eafd9c27054b02d0f8b30fe64
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98454
Analysis date: Sat, 24 Oct 2026 07:12:19 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A malicious SMB server can make the client parse bytes outside an individual create context as file-ID or lease data, potentially causing incorrect state or a kernel fault without a demonstrated write or sensitive disclosure.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98454 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98454

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 7.0
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-2026-98454	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98454 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE_KPANIC, Aegis: MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-130;Other CVSS 'AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L';BEST CVSS score: '7.6';DESCR 'The SMB client validates the complete create context area but previously did not confine each record to the boundary specified by its Next field. A malicious or compromised SMB server can return a malformed SMB2 or SMB3 create response that makes QFid or lease handlers read bytes outside the current context and potentially beyond a short terminal record. Lease fields could be taken from unrelated memory because the parsers used canonical structure offsets instead of DataOffset and accepted an invalid DataLength. For the CVSS the PR:N value is selected because the attacking SMB server needs no authenticated privilege on the client once the client processes its response. User interaction is required because a user or administrator normally must connect to or mount the attacker controlled share. The supported primitive is an out of bounds read rather than an out of bounds write. Impact can include limited information exposure, incorrect lease or caching state, and a possible kernel crash. There is no supported arbitrary write or direct privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.6 and the production ActionableScore returned 4 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 ActionableScore threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	OOB DISK SKIP SERVERTOCLIENT LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 4; no floor or cap applied.
* Raw paranoid score: 4.
* Paranoid score: 4; stronger effects require unsupported disclosure or write assumptions.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Remote/network reachability: an attacker-controlled SMB server can return malformed create contexts after the client connects.
* +1 Weak/indirect corruption concern: malformed offsets and lengths cause handlers to consume bytes outside the current context as `DiskFileId`, `LeaseState`, `LeaseFlags`, or `Epoch`.
* +1 Plausible kernel crash: the patch confirms out-of-bounds reads; a sufficiently short terminal context can plausibly fault.
* No confidentiality point: no sensitive kernel bytes are shown reaching userspace or the network. Wrong `IndexNumber` or lease values alone do not establish disclosure.
* No integrity point: incorrect lease/caching state is possible, but no unauthorized protected-state modification is demonstrated.
* No write, UAF, retry-accumulated OOB write, shared-backing write, authorization bypass, arbitrary access, or LPE is shown.
* No extra availability point: it would duplicate the same possible OOB-read fault.

3. Reachability analysis

The attacking principal is a malicious or compromised SMB server with no client-host privilege. Victim interaction is needed to connect to or access the share, but the malformed response itself does not require host UID 0 or host-administrator capability. Mount/setup details may vary, but they are performed by the victim rather than granting privilege to the remote attacker. No namespace capability, special hardware, race, or unusual boot configuration is implicated.

4. Primitive and severity reading

The exact primitive is an attacker-influenced out-of-bounds or cross-record read from a validated SMB response buffer, followed by use of the resulting values as file identity or lease metadata. This is read-only invalid-state consumption, not heap corruption or a strong semantic-reinterpretation primitive. The patch supports malformed state and possible crash; sensitive disclosure, persistent cache corruption, arbitrary write, and privilege escalation remain unproven. Therefore this is CLASS_C, not an Important-preserving Class B/A case. Auto-downgrade remains allowed, although manual validation of terminal-record bounds and user-visible propagation is advisable.

5. One-sentence report phrase

A malicious SMB server can make the client parse bytes outside an individual create context as file-ID or lease data, potentially causing incorrect state or a kernel fault without a demonstrated write or sensitive disclosure.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm whether any terminal-record OOB bytes can propagate through `IndexNumber` to userspace or produce a reliable kernel fault.

7. Call-site confidence

Call-site confidence: medium

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

Patch: smb: client: fix create context out-of-bounds reads
Commit: e4c49012708c917eafd9c27054b02d0f8b30fe64
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e4c49012708c917eafd9c27054b02d0f8b30fe64

Commit description:

smb2_parse_contexts() validates the complete create-context area but
does not limit each record to its Next field before dispatching it.  A
malformed chain can therefore expose bytes beyond the current context to
a handler.  The QFid handler also used a full response-structure cast
although it only reads DiskFileId.

The SMB2/SMB3 lease parsers made the same layout assumption: they read
LeaseState and LeaseFlags at canonical offsets rather than at
DataOffset.  A valid non-canonical DataOffset could therefore yield
unrelated in-bounds data, while a short DataLength was still accepted.

Limit each context to its Next value, reject offsets before the context
header, and reject malformed chains.  Bound the name range by the current
context and do not dispatch a known handler when DataLength is zero.  Read
the QFid DiskFileId only when the context data covers that field.  Parse the
lease context from DataOffset and require DataLength to match the v1 or v2
lease_context size used by ksmbd.  A size mismatch skips lease parsing
without failing the open.

Fixes: b8c32db ("CIFS: Request SMB2.1 leases")
Fixes: f047390 ("CIFS: Add create lease v2 context for SMB3")
Fixes: 89a5bfa ("smb3: optimize open to not send query file internal info")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: LLM
Co-developed-by: Luxing Yin <root@tr0jan.top>
Signed-off-by: Luxing Yin <root@tr0jan.top>
Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
Tested-by: Frank Sorenson <sorenson@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/smb2ops.c
  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=e4c49012708c917eafd9c27054b02d0f8b30fe64

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

The original Linux kernel CVE announcement for CVE-2026-98454 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98454

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:L/I:L/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 7.6

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: 4

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).