[CVE-2026-98405][MODERATE 7.0] smb: client: fix missing iov bounds check in parse_posix_sids()

[CVE-2026-98405][MODERATE 7.0] smb: client: fix missing iov bounds check in parse_posix_sids()

[AL-KERNEL]

CVE: CVE-2026-98405
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: fix missing iov bounds check in parse_posix_sids()
Commit: d91b9a3b2b38e5ac1b51e9e5b23fe53ad7b49644
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d91b9a3b2b38e5ac1b51e9e5b23fe53ad7b49644
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98405
Analysis date: Wed, 14 Oct 2026 22:45:42 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
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-2026-98405 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98405

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

CVE-2026-98405	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98405 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC)	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:L/A:H';CWE-125;*CWE-20;CWE-190;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'The SMB client parse_posix_sids path calculates sidsbuf_end from the server supplied out_len without first validating it against the actual received iov length. A malicious or compromised SMB server can provide an inflated length and make posix_info_sid_size read beyond the response buffer into adjacent kernel memory. This may cause a kernel crash or invalid SID parsing and therefore represents a remotely triggerable availability risk for clients connected to an attacker controlled server. For the CVSS the PR:N value is used because the attacker does not need credentials or local privileges on the affected client and only needs control of the SMB server response. AV:N is used because the malformed response can be delivered over a routed SMB connection. The base impact is denial of service because no direct return path for the out of bounds kernel data is demonstrated. The paranoid impact is C:L/I:L/A:H because adjacent kernel data may be consumed during SID parsing and the resulting metadata handling requires manual review for secondary confidentiality or integrity effects. The issue does not justify CIA:HHH because the available primitive is an out of bounds read rather than an arbitrary write or a demonstrated use after free. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 8.6 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 MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. 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 produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 5.3 and ActionableScore 3 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. 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 SIMPLEFIX SERVERTOCLIENT LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3
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 conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +2 Remote reachability. A malicious or compromised SMB server controls `out_len` in a response processed by an already connected SMB client.
* +1 Weak corruption concern. The inflated length defeats the intended parser boundary and produces a confirmed kernel out-of-bounds read.
* Total: 3.

Paranoid signals:

* +2 Remote reachability.
* +1 Confirmed kernel out-of-bounds read.
* +1 Realistic kernel fault or strong DoS. A sufficiently extended parser boundary can make SID parsing access unmapped or invalid adjacent memory, although the supplied patch does not demonstrate a specific panic.
* Total: 4.

Not awarded:

* No OOB-write or other write primitive is established.
* No UAF, stale lifetime operation, controlled reclaim, or arbitrary access exists.
* No confidentiality point is awarded because bytes read beyond the iov are not shown to be returned to the server, userspace, or another observer.
* No integrity point is awarded because incorrect SID parsing is possible, but modification of a protected object or authorization decision is not established.
* No additional availability point is awarded for the same potential kernel fault.
* B5-R does not apply because requirement 1 fails. This is an OOB read, not a retry-accumulated heap OOB write.
* B3-PENDING does not apply because there is no shared-backing write.
* B4-PENDING does not apply because no authorization guard changes from DENY to ALLOW.

3. Reachability analysis

The relevant attacker is a malicious or compromised SMB server that sends an inflated `out_len` in a response consumed by the Linux SMB client. Once a client connection and the affected operation exist, the attacker needs neither host UID 0 nor host-administrator capabilities.

An SMB mount or connection is a prerequisite and may have been configured by another local actor, but the vulnerable response itself requires no attacker-controlled local configuration. The complete trigger does not depend on a user namespace capability. Namespace scoping is therefore irrelevant to the remote trigger and remains unknown as a deployment property.

No special hardware, boot option, race, or timing window is indicated. Practical exposure requires use of the affected SMB POSIX owner or group parsing path, including the reparse-point-related functionality identified by the fixing commit.

4. Primitive and severity interpretation

The exact primitive is a server-controlled kernel out-of-bounds read. `sidsbuf_end` is derived from untrusted `out_len` without being bounded by `rsp_iov->iov_len`, so `posix_info_sid_size()` can treat memory beyond the received response as valid SID input.

This is not a lifetime violation and is neither active structured-object UAF nor fixed stale storage. There is no repeated release or refcount mutation.

The primitive is CLASS_C because the established behavior is invalid kernel memory consumption with plausible crash or malformed parsing, but without an independently useful disclosure, write, authorization bypass, or object-lifetime primitive. Incorrect owner or group SID interpretation is worth reviewing, but the supplied call path does not establish that it reaches a protected authorization decision or persistent metadata update.

ImportantCandidate is NO because neither Class A nor a strong unresolved Class B primitive exists. AutoDowngradeAllowed is YES because the confirmed primitive remains a limited OOB read without a demonstrated disclosure, write, protected-resource impact, or security-boundary bypass. Operationally this is a remotely reachable borderline Moderate issue for SMB clients connected to an attacker-controlled server.

5. One-sentence report phrase

A malicious SMB server can inflate a response length so that parse_posix_sids reads beyond the received iov, potentially causing invalid SID parsing or a kernel crash without a demonstrated disclosure or write primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the downstream use of parsed owner and group SIDs to confirm that adjacent kernel bytes cannot affect a protected authorization decision, become externally observable, or produce a persistent metadata integrity consequence.

7. Call-site confidence

Call-site confidence: medium

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

Patch: smb: client: fix missing iov bounds check in parse_posix_sids()
Commit: d91b9a3b2b38e5ac1b51e9e5b23fe53ad7b49644
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d91b9a3b2b38e5ac1b51e9e5b23fe53ad7b49644

Commit description:

In parse_posix_sids(), sidsbuf_end is calculated using the server-supplied
out_len without being validated against the actual length of the received
iov (iov_len).

If a server provides an inflated out_len, sidsbuf_end will point past the
end of the iov. This defeats the bounds guards in posix_info_sid_size(),
allowing out-of-bounds reads into adjacent kernel memory.

Fix this by rejecting responses where the calculated sidsbuf_end would
exceed the received iov boundaries or cause pointer wraparound.

Fixes: a90f37e ("smb: client: parse owner/group when creating reparse points")
Cc: stable@vger.kernel.org
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/smb2inode.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=d91b9a3b2b38e5ac1b51e9e5b23fe53ad7b49644

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

The original Linux kernel CVE announcement for CVE-2026-98405 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98405

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:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 3
  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).