* [CVE-2026-99280][MODERATE 7.0] ksmbd: drain session procfs readers before dropping table references
@ 2026-11-08 2:22 21% AL-KERNEL
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From: AL-KERNEL @ 2026-11-08 2:22 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99280
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ksmbd: drain session procfs readers before dropping table references
Commit: 6789f0983f8e85ce3a5ed8c50fc05d613ead9c2c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6789f0983f8e85ce3a5ed8c50fc05d613ead9c2c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99280
Analysis date: Sat, 07 Nov 2026 22:22:18 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A race between ksmbd session cleanup and procfs readers can traverse a freed file-table IDR or self-deadlock during final session reference release.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99280 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99280
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-2026-99280 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99280 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-362;*CWE-416;*CWE-833;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in ksmbd session lifetime handling can leave a per session procfs callback active while registration failure or connection cleanup drops the table reference. If that reader owns the final reference, its final put can call proc_remove from inside the same callback and wait for itself, causing a deadlock and service denial of service. Previous session replacement can also free the file table IDR while session_open_file_count is traversing it, providing a concrete use after free read candidate that may cause a kernel crash. For the CVSS the PR:L value reflects that reliable exploitation requires a local user or process able to read the ksmbd procfs entry and coordinate it with session cleanup. A remote SMB client may influence session replacement or disconnection, but remote reachability alone is not sufficient. AC:H is used because the attacker must hit a narrow concurrent cleanup and procfs reading window. The base impact is availability loss, while the paranoid score allows limited confidentiality and integrity impact from traversal of freed and potentially reused IDR memory without claiming an arbitrary write or proven privilege escalation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.8 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 manual review requirement was applied. KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation 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_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.4 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. 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 DISK LEAK SKIP LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 4. REAL UAF FLOOR 4 raises 2 -> 4.
* Raw paranoid score: 2.
* Paranoid score: 4. No technically supported additional primitive; FLOOR 4 raises 2 -> 4.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 Real UAF: `ksmbd_destroy_file_table()` could destroy and free `ft->idr` while `session_open_file_count()` traversed it.
* +1 Reliable DoS: the stale IDR traversal can fault; separately, a final session put can invoke `proc_remove()` from its own procfs callback and deadlock.
* -1 Hard race: exploitation requires coordinating a procfs reader with session replacement, registration failure, or connection cleanup during a narrow lifetime window.
* No extra availability point: crash and deadlock are alternative manifestations of the same availability impact.
* No structured-stale leverage: IDR traversal is nontrivial, but attacker-controlled reclaim, replacement contents, pointers, or a later write are not shown.
* No repeated-release point: the patch does not establish two lifetime-mutating operations through the exact same dangling reference.
* No confidentiality or integrity point: traversal of freed IDR storage does not itself establish disclosure or modification.
* NEW52/B5-R does not apply: no retry-accumulated heap OOB write exists.
* No authorization bypass or B4-PENDING mechanics are present.
3. Reachability analysis
The supplied summary supports a below-host-admin local process reading the per-session procfs entry while influencing session cleanup, so `HostAdminRequired=NO`. Exact procfs ownership/mode and any namespace capability scope are not supplied; numeric host UID 0 and namespace-scoped privilege therefore remain unresolved. A remote SMB client may influence replacement or disconnect, but remote-only triggering and coordination of the procfs reader are not established. No special hardware or boot mode is required.
4. Primitive and severity reading
The principal primitive is a race-driven read-side UAF of an active IDR during procfs file-count traversal. The fix detaches the IDR under `file_table.lock`, causing readers to report zero before destruction. A separate session/procfs lifetime ordering bug can self-deadlock.
This is CLASS_B because a real structured-object lifetime violation exists, but the shown consequences are stale traversal, crash, and deadlock. There is no OOB write, controlled reclaim, disclosure path, callback control, or authorization boundary bypass. Accordingly, Important-grade leverage is not demonstrated or specifically preserved, and constrained Moderate downgrade remains permissible after review.
5. One-sentence report phrase
A race between ksmbd session cleanup and procfs readers can traverse a freed file-table IDR or self-deadlock during final session reference release.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm procfs permissions, whether one below-host-admin actor can reliably drive both sides of the race, and whether stale IDR traversal reaches any effect beyond faulting.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ksmbd: drain session procfs readers before dropping table references
Commit: 6789f0983f8e85ce3a5ed8c50fc05d613ead9c2c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6789f0983f8e85ce3a5ed8c50fc05d613ead9c2c
Commit description:
Session registration failure and connection cleanup can drop the table
reference while the per-session procfs entry is still accessible. If a
reader holds the last remaining reference, its final put calls
proc_remove() from its own callback and waits for that callback to
finish.
Remove the procfs entry before dropping the table reference in the
registration failure path. Queue sessions removed during connection
cleanup and drain their procfs readers after releasing both session
locks, then return their table references. Keep the global hash node
unhashed while a session is queued so a concurrent unregister cannot
drop the reference again.
Previous-session replacement also destroys the file table before the
session is finally freed. Detach the idr under the lock used by procfs
file counters, and report zero files after it has been detached. This
prevents a reader from accessing the idr during or after its
destruction.
Fixes: d7fd1f9 ("ksmbd: follow SMB2 session expiration semantics")
Cc: [email protected]
Reported-by: Abdifatah Suruur <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/smb/server/mgmt/user_session.c
fs/smb/server/vfs_cache.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=6789f0983f8e85ce3a5ed8c50fc05d613ead9c2c
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99280 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99280
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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 5.8
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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