[CVE-2026-97986][MODERATE 7.0] virtio_input: stop callbacks before unregistering input device [ Upstream

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

CVE: CVE-2026-97986
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: virtio_input: stop callbacks before unregistering input device [ Upstream
Commit: 8226aeee9b9a94cd699fbb51cb230feff46cfaf2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8226aeee9b9a94cd699fbb51cb230feff46cfaf2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97986
Analysis date: Fri, 25 Sep 2026 12:37:20 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97986 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97986

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-2026-97986	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97986 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;*CWE-416;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur in the virtio input driver because virtinput_remove unregisters and may free vi->idev before virtio device callbacks are stopped. A callback that passed the vi->ready check can drop the lock around input_event and later resume using vi->idev while also requeueing buffers and kicking the virtqueue. This can cause kernel memory corruption, at least a guest kernel crash, and potentially confidentiality integrity or privilege impact if the stale object is reused in a controllable way. For the CVSS the PR:L in the paranoid score reflects environments where a reduced capability service account, container root, or virtual machine management user can influence virtio device reset or removal without full host administration. The issue is not directly network reachable. Exploitation depends on local or virtualization control of the virtio device lifecycle and on callback timing. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	VIRT INIT SIMPLEFIX HARDWARE LINUS PACKET  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative floor: 3 -> 4. A real UAF reaches an active input device object and host-admin-equivalent privilege is not positively established.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF / active lifetime violation. `input_unregister_device()` can free `vi->idev` while `virtinput_recv_events()` has an in-flight callback that already passed the `vi->ready` check and can still call `input_event()` using `vi->idev`.
* +1 Reliable kernel crash / strong DoS. Dereferencing a freed `struct input_dev` through the callback can plausibly cause a kernel fault or memory-safety failure.
* +0 No attacker-controlled reclaim, object replacement, arbitrary write, callback hijack, disclosure, or privilege escalation is established by the patch.
* +0 Structured stale-object leverage is not awarded. `vi->idev` is an active structured object, but the supplied evidence does not establish attacker control of post-free replacement contents or meaningful field consumption after controlled reuse.
* +0 Local unprivileged trigger is not awarded. The patch does not establish that an ordinary guest user can initiate the required virtio device removal or reset sequence.
* +0 Firmware-mediated external influence is not awarded. The patch identifies callback behavior but does not establish that an untrusted device backend can independently cause the complete removal and callback race.
* -0 No host-admin penalty is applied. Host-admin-equivalent privilege is not proven, but below-host-admin reachability is also not proven.
* -0 No hard-race penalty is applied. The bug is concurrent teardown versus callback execution, but the supplied material does not prove a narrow, one-shot, or externally uncontrollable timing window.
* +0 No additional Availability point is awarded. The possible kernel crash is already counted as the strong DoS signal.
* +0 Confidentiality and integrity impact are not awarded. A UAF exists, but no read-back path, protected-state modification, controlled reuse, or directed write is established.

3. Reachability analysis

The vulnerable sequence requires a virtio input callback to overlap device removal. The callback enters `virtinput_recv_events()`, passes the initial `vi->ready` check, drops `vi->lock` around `input_event()`, and later resumes after `virtinput_remove()` has unregistered and potentially freed `vi->idev`.

The patch does not establish which security principal can reliably invoke the complete device removal or reset path. A host virtualization administrator, VMM, device backend, or privileged guest device-management actor may be able to influence this lifecycle, but the supplied context does not prove that an ordinary guest user, a container user, or a namespace-scoped capability holder can perform the entire sequence.

No direct network trigger is established. This is not a packet-processing vulnerability and should not be treated as AV:N merely because virtio may be used in virtualized deployments. No special physical hardware requirement is shown beyond the presence of a virtio input device and a transport with callbacks not fully covered by the existing evdev RCU grace period behavior.

4. Primitive and severity interpretation

The patch establishes a real callback-versus-teardown use-after-free. `vi->idev` is an active structured `input_dev` object, not merely a fixed stale DMA buffer. However, the demonstrated stale operation is a callback path using `input_event()` during device teardown, and no controlled object replacement, attacker-shaped post-free contents, refcount takeover, arbitrary kernel read/write, or function-pointer influence is shown.

This is not a repeated release or refcount mutation case. `input_unregister_device()` may end the lifetime of `vi->idev`, but the later stale operation is a dereference through `input_event()`, not a second concrete `put`, `free`, or refcount decrement on the exact same dangling reference.

PrimitiveClass is CLASS_B because an actual UAF/lifetime violation is directly established. The demonstrated practical consequence is guest kernel crash or DoS. Memory corruption beyond the fault is possible in principle, but meaningful exploitation leverage is not established by the supplied patch. ImportantCandidate is therefore NO, while ManualReview remains RECOMMENDED because the lifetime violation affects a kernel input object and callback synchronization differs across virtio transports.

AutoDowngradeAllowed is YES because this is presently a constrained callback-teardown UAF with no established controlled reuse, repeated lifetime mutation, security-boundary bypass, or below-host-admin attacker path.

5. One-sentence report phrase

A virtio input callback can dereference a freed input device during device removal because unregistering the device occurs before callbacks are stopped, causing a potential guest kernel crash or denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether a below-host-admin guest actor, delegated VMM service, or untrusted virtio backend can reliably trigger device removal or reset while controlling callback delivery. If such reachability and post-free object influence are established, the issue should be re-evaluated as an Important candidate.

7. Call-site confidence

Call-site confidence: medium

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

Patch: virtio_input: stop callbacks before unregistering input device [ Upstream
Commit: 8226aeee9b9a94cd699fbb51cb230feff46cfaf2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8226aeee9b9a94cd699fbb51cb230feff46cfaf2

Changed files:
  drivers/virtio/virtio_input.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=8226aeee9b9a94cd699fbb51cb230feff46cfaf2

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

The original Linux kernel CVE announcement for CVE-2026-97986 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97986

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).