[CVE-2026-99277][MODERATE 7.0] ksmbd: hold a connection reference for each session channel

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

CVE: CVE-2026-99277
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ksmbd: hold a connection reference for each session channel
Commit: 4b333aed69cfc2c8687b86b6a4364a0dffc16dd8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b333aed69cfc2c8687b86b6a4364a0dffc16dd8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99277
Analysis date: Sat, 07 Nov 2026 22:02:34 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
An authenticated SMB client can race session and connection teardown so a live channel later accesses a freed ksmbd connection object.

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

The original Linux kernel CVE announcement for CVE-2026-99277 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99277

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-2026-99277	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99277 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race in ksmbd session and connection lifetime management can leave a session channel holding a raw pointer to a freed ksmbd connection. A concurrent session reference holder may access chann conn after connection cleanup can no longer find the unpublished session, including during SMB3.1.1 channel binding or a procfs read. This is a use after free candidate with kernel crash impact and a plausible worst case memory corruption consequence if the freed connection allocation is reused. For the CVSS the PR:L value is selected because the practical network trigger normally requires an established SMB session rather than only unauthenticated reachability. AC:H reflects the required race between session use, unregister, and connection cleanup. SMB is commonly exposed on local or enterprise networks, while direct public Internet exposure is less typical. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.5 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. 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 3.1 and ActionableScore 5 with primitive class CLASS_B and manual review REQUIRED. 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 Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	REMOTE DISK LEAK UAF SKIP LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 4; the real-UAF floor of 4 does not change it.
* Raw paranoid score: 5.
* Paranoid score: 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 — Real active-object UAF: a session channel retains a raw `ksmbd_conn` pointer after connection cleanup can free that connection.
* +2 — Network reachability: an authenticated SMB client can plausibly exercise concurrent SMB3.1.1 binding/session activity.
* +1 — Plausible kernel crash/host DoS from dereferencing the freed connection.
* -1 — The supplied evidence explicitly requires a high-complexity race among session unregister, retained session references, and connection cleanup.
* Paranoid +1 — authenticated clients can plausibly repeat connection/session lifecycle and binding operations, materially increasing attempts at the vulnerable lifetime sequence. This does not establish controlled reclaim.

Not awarded: controlled reclaim, attacker-shaped replacement contents, arbitrary read/write, callback control, confidentiality, integrity, LPE, or a second availability point. The procfs path is another stated consumer, not a separate score. No authorization decision is bypassed.

3. Reachability analysis

The grounded attacker is a remote SMB client with an established session, not host UID 0 or host administrator. No namespace capability or prior privileged setup is indicated. The complete race mechanics are credible from the commit, although exact timing control and reliability are not shown. SMB authentication supports PR:L-like exposure but does not confer host administrative power.

4. Primitive and severity reading

This is an active structured-object lifetime violation: the channel remains alive and later kernel processing consumes `chann->conn` after the connection may have been freed. The patch adds a connection reference at channel registration and releases it at every channel-removal path, directly restoring the missing lifetime invariant.

The shown effects are UAF and plausible host crash. Reuse-based corruption is possible but unproven. Nevertheless, an attacker-influenced network session lifecycle, a privileged kernel consumer, and the SMB-client-to-host trust boundary form a specific unresolved cross-boundary active-state chain. Therefore this remains CLASS_B, ImportantCandidate=YES, with no automatic downgrade.

5. One-sentence report phrase

An authenticated SMB client can race session and connection teardown so a live channel later accesses a freed ksmbd connection object.

6. Manual review advice

MANUAL CHECK REQUIRED

Review stale `ksmbd_conn` field consumption during channel binding and response signing, plus whether remote lifecycle control permits useful reclaim or writes beyond a crash.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ksmbd: hold a connection reference for each session channel
Commit: 4b333aed69cfc2c8687b86b6a4364a0dffc16dd8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b333aed69cfc2c8687b86b6a4364a0dffc16dd8

Commit description:

ksmbd_session_unregister() removes a session from the global and per-
connection tables before dropping the table reference. A concurrent
reference holder can keep the session and its channel list alive after
those removals.

Connection cleanup can no longer find the unpublished session to remove its
channels. Since a channel only stores a raw conn pointer, the connection
can be freed while another session reference holder is still accessing it,
for example during SMB3.1.1 binding or a procfs read.

Take a connection reference when registering a channel and release it on
insertion failure, channel removal, or final session destruction. Keep the
channels and signing keys until the session is destroyed so a response can
still be signed after the session has been unregistered.

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/mgmt/user_session.c
  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=4b333aed69cfc2c8687b86b6a4364a0dffc16dd8

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

The original Linux kernel CVE announcement for CVE-2026-99277 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99277

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 4
  Paranoid ActionableScore: 5

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).