[CVE-2026-99278][MODERATE 7.0] ksmbd: limit sessions on each connection

[CVE-2026-99278][MODERATE 7.0] ksmbd: limit sessions on each connection

[AL-KERNEL]

CVE: CVE-2026-99278
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ksmbd: limit sessions on each connection
Commit: 94f8462fc9d5332bc54e91605003c17381e9171a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=94f8462fc9d5332bc54e91605003c17381e9171a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99278
Analysis date: Sat, 07 Nov 2026 22:20:17 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
An authenticated remote SMB client can retain an unbounded number of valid ksmbd sessions on one connection, causing attacker-driven memory consumption and potential denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-99278 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99278

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.

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

CVE-2026-99278	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99278 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:L/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-770;*CWE-772;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.5';DESCR 'A resource accounting flaw in ksmbd allowed an authenticated network client to complete authentication repeatedly and retain an unbounded number of Valid SMB sessions on one connection because the existing pending setup limit counted only InProgress sessions. Repeated exploitation can retain kernel session objects and associated resources until memory pressure degrades ksmbd or causes a broader denial of service. For the CVSS the PR:L value is selected because reliable triggering normally requires an account or equivalent authorization that can successfully complete SMB authentication. The demonstrated primitive is persistent resource retention with no evidence of UAF, OOB access, information disclosure, or an arbitrary write. The base impact is A:L because substantial exhaustion requires sustained repetition. The paranoid impact is A:H because the accumulation is attacker controlled and lacked a per connection bound. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.5 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 5.3 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	REMOTE OOB DISK INIT LEAK SKIP LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=NONE
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: 4.
* Paranoid score: 4; no floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* **+2 remote network reachability:** An authenticated SMB client can repeatedly invoke session setup over one connection.
* **+1 attacker-driven unbounded resource accumulation:** Completed sessions become `Valid` and escape the old pending-setup limit, retaining session objects and associated resources.
* **Paranoid +1 broader DoS:** Sustained accumulation can plausibly produce severe memory pressure and broader service or host availability loss. A kernel panic is not shown.
* No UAF, OOB access/write, stale-object use, arbitrary write, disclosure, ownership breach, or persistent orphaned reference is shown.
* No authorization bypass: authentication still must succeed; the defect is missing resource accounting, not a DENY-to-ALLOW security decision.
* NEW52 B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of corrupted structured state.
* No additional availability point in the base score because concrete host-wide failure is not demonstrated.

3. Reachability analysis

The supported attacker is a remote client with an account or equivalent credentials sufficient to complete SMB authentication repeatedly. This is below host-administrator privilege and requires neither host UID 0 nor a namespace capability. No special hardware, race, boot option, or prior privileged per-attacker setup is shown beyond operation of an exposed ksmbd service.

4. Primitive and severity reading

The exact defect is absent per-connection accounting for completed SMB sessions. The patch reserves a slot before allocation and releases it on failures, channel removal, or final destruction. This bounds attacker-retained valid objects but does not repair memory corruption or a true lost-reference leak. Shown impact is resource growth and service degradation; severe host-wide exhaustion remains plausible but not demonstrated. Therefore the issue is `NONE`, not Class B/A, and does not warrant Important preservation or blocking an evidence-based Moderate downgrade.

5. One-sentence report phrase

An authenticated remote SMB client can retain an unbounded number of valid ksmbd sessions on one connection, causing attacker-driven memory consumption and potential denial of service.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm practical per-session memory cost, cleanup behavior, authentication throttling, and whether sustained sessions can exhaust host memory rather than only degrading ksmbd.

7. Call-site confidence

Call-site confidence: high

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

Patch: ksmbd: limit sessions on each connection
Commit: 94f8462fc9d5332bc54e91605003c17381e9171a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=94f8462fc9d5332bc54e91605003c17381e9171a

Commit description:

The pending setup limit only counts InProgress sessions. A client can
complete authentication repeatedly and retain an unbounded number of Valid
sessions on one connection.

Reserve a connection slot before allocating a session and retain a
connection reference while authentication is in progress. The first SMB3
channel takes over that reservation; binding to another connection reserves
one slot there. Reauthentication and authentication continuation reuse the
existing reservation. Return slots on allocation or insertion failure,
channel removal, and final session destruction.

Accept max_sessions_per_connection in reserved startup-request space and
default to 64 when older tools leave it zero. Keep the request size and
existing field offsets unchanged. Expose the configured limit in procfs.
The existing connection limits bound the aggregate number of sessions
without a separate global session allocation limit.

Fixes: d7fd1f9 ("ksmbd: follow SMB2 session expiration semantics")
Cc: stable@vger.kernel.org
Reported-by: Abdifatah Suruur <suruurism@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/server/connection.c
  fs/smb/server/connection.h
  fs/smb/server/ksmbd_netlink.h
  fs/smb/server/mgmt/user_session.c
  fs/smb/server/mgmt/user_session.h
  fs/smb/server/proc.c
  fs/smb/server/server.c
  fs/smb/server/server.h
  fs/smb/server/smb2pdu.c
  fs/smb/server/transport_ipc.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=94f8462fc9d5332bc54e91605003c17381e9171a

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

The original Linux kernel CVE announcement for CVE-2026-99278 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99278

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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).