[CVE-2026-99216][LOW] Drivers: hv: Don't reset VMBus connection state on error/exit paths [ Upstream

[CVE-2026-99216][LOW] Drivers: hv: Don't reset VMBus connection state on error/exit paths [ Upstream

[AL-KERNEL]

CVE: CVE-2026-99216
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: Drivers: hv: Don't reset VMBus connection state on error/exit paths [ Upstream
Commit: f47ce27af80b87cc684d5c12b65506af498ac7e5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f47ce27af80b87cc684d5c12b65506af498ac7e5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99216
Analysis date: Fri, 30 Oct 2026 10:54:38 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Prematurely marking VMBus disconnected can suppress actual connection teardown and leave host messages or interrupts active during guest cleanup, with disruption possible but no demonstrated memory corruption or panic.

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

The original Linux kernel CVE announcement for CVE-2026-99216 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99216

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-99216	LOW	https://www.kernelcve.org/list/?q=CVE-2026-99216 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-404;CWE-459;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A VMBus lifecycle logic error marks the connection as DISCONNECTED before vmbus_disconnect checks whether an active connection must be unloaded. This can leave the Hyper V connection active after a connection failure or during driver exit, allowing the host to continue sending messages or posting VMBus interrupts while guest cleanup is in progress. The demonstrated primitive is incomplete teardown and continued asynchronous activity rather than a proven UAF, OOB access, or arbitrary write. For the CVSS the PR:N value in the paranoid vector reflects that a Hyper V host can generate VMBus events without privileges inside the guest once the guest enters the affected cleanup path. AC:H reflects the required error or exit state and the unresolved timing between host events and guest teardown. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	INIT LEAK LINUS KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; no floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* **+1 weak/indirect lifecycle-state defect:** setting `conn_state` to `DISCONNECTED` causes `vmbus_initiate_unload()` to skip unloading an actually remaining connection. Host messages or interrupts may therefore continue during cleanup.
* **Paranoid +1 availability concern:** continued asynchronous host activity after guest teardown begins plausibly permits guest disruption. The patch does not establish a reliable panic, so this is retained only in the paranoid score.
* No UAF, OOB access, repeated release, refcount mutation, arbitrary write, controlled reclaim, disclosure, or authorization bypass is shown.
* No extra crash or availability point is awarded: a host-wide crash is not demonstrated.
* B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of corrupted heap state.
* B3-PENDING does not apply: no shared-backing write exists.
* B4-PENDING does not apply: the connection-state check is a lifecycle guard, not an authorization DENY-to-ALLOW decision.

3. Reachability analysis

The vulnerable paths are VMBus connection-failure cleanup and driver exit. A Hyper-V host can continue generating VMBus messages or interrupts after the guest reaches either path, but the evidence does not show that an attacker can independently force the complete failure/exit sequence. Driver exit may require privileged guest administration, while connection failure may be host-influenced; the supplied evidence does not resolve this split. No namespace-scoped trigger is shown. Hyper-V virtualization is required, but no rarity penalty is applied.

4. Primitive and severity reading

The exact primitive is incomplete retirement of an active VMBus connection caused by prematurely changing its state before the disconnect routine checks it. This is invalid active-state/teardown behavior, classified as **CLASS_C**, not a demonstrated memory-lifetime violation. The shown consequence is continued host-to-guest asynchronous activity; guest panic, stale-memory access, corruption, or escape remains unproven. Consequently, there is no Important-class primitive and automatic downgrade remains allowed.

5. One-sentence report phrase

Prematurely marking VMBus disconnected can suppress actual connection teardown and leave host messages or interrupts active during guest cleanup, with disruption possible but no demonstrated memory corruption or panic.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm whether host-driven messages can reach handlers after their supporting guest state is destroyed or cause a reproducible guest-wide failure.

7. Call-site confidence

Call-site confidence: medium

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

Patch: Drivers: hv: Don't reset VMBus connection state on error/exit paths [ Upstream
Commit: f47ce27af80b87cc684d5c12b65506af498ac7e5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f47ce27af80b87cc684d5c12b65506af498ac7e5

Changed files:
  drivers/hv/connection.c
  drivers/hv/vmbus_drv.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=f47ce27af80b87cc684d5c12b65506af498ac7e5

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

The original Linux kernel CVE announcement for CVE-2026-99216 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99216

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 1
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).