[CVE-2026-93200][MODERATE 7.0] i3c: master: Fix use-after-free of master->this [ Upstream

[CVE-2026-93200][MODERATE 7.0] i3c: master: Fix use-after-free of master->this [ Upstream

[AL-KERNEL]

CVE: CVE-2026-93200
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: i3c: master: Fix use-after-free of master->this [ Upstream
Commit: 4f3145db05fede36b35f8249b8acde5bd5d54864
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f3145db05fede36b35f8249b8acde5bd5d54864
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93200
Analysis date: Thu, 17 Sep 2026 17:49:51 -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-2026-93200 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93200

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-2026-93200	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93200 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-825;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in the I3C master controller sysfs path because sysfs attribute callbacks may dereference the master self descriptor after it has already been freed during device detach. A local user can potentially trigger the vulnerable access by reading the exposed sysfs attributes while the controller is being torn down or unbound, causing a stale kernel pointer dereference. For the CVSS the PR:L is used for the paranoid score because local code execution or local sysfs access is needed, but full administrative privileges are not necessarily required for the sysfs read side of the race. The issue is not network reachable and depends on I3C support and a reachable master controller device. Impact is at least local denial of service via kernel crash. In the paranoid interpretation, the UAF should be treated as possible kernel memory corruption with potential confidentiality, integrity, and availability impact, so manual review is warranted.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	INIT ERRORPATH UAF HARDWARE KPANIC 	YES	NO	checked

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

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

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

Conservative floor applied: 2 -> 4 due to a real kernel UAF with stale reference use and no positively established host-admin-only requirement.
Paranoid floor applied: 3 -> 4. No floor 5 was applied because controlled reclaim, repeated lifetime mutation, attacker-shaped replacement, or security-boundary impact is not established.

2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation. The commit directly states that sysfs callbacks dereference master->this after it was freed in i3c_master_detach_free_devs().
* +1 Reliable kernel crash / strong DoS in paranoid scoring. A sysfs callback dereferencing a freed kernel object can plausibly fault or trigger KASAN/Oops.
* +0 Conservative crash signal kept limited. The patch proves UAF, but the supplied context does not show an observed panic trace.

Negative signals:

* -1 Hard teardown timing in conservative scoring. The vulnerable access requires overlap between sysfs access and master-controller teardown/release ordering.
* No host-admin -2 penalty. Complete host-admin requirement is not positively established.
* No rare hardware penalty. I3C hardware is device-specific, but the supplied evidence is insufficient to classify it as physical-only or rare enough for a scoring penalty.

Non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded merely because UAF exists.
* Remote reachability not established.
* Local unprivileged trigger not awarded because the complete trigger chain likely also requires controller teardown/unbind, and below-host-admin control of that stage is not established.
* Structured stale-object leverage not awarded because the shown stale path is sysfs dereference of master->this without evidence of attacker-controlled replacement contents or security-relevant post-reuse field consumption.
* Concrete repeated release/refcount signal not awarded. The patch delays freeing master->this, but does not show first release then exact same dangling reference receiving a second lifetime/refcount mutation.
* Weak LPE not awarded solely from UAF.
* Extra availability not awarded because it would double-count the same crash/fault consequence.

Repeated release/refcount checklist:

* First release can end lifetime: yes, kfree(master->this) can free the object.
* Exact same reference survives: yes, master->this can remain reachable to sysfs callbacks.
* Second operation is a real lifetime/refcount mutation: no, the described stale operation is dereference by sysfs callbacks, not another put/free/refcount mutation.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.

3. Reachability analysis

The vulnerable reader is a sysfs attribute callback for the I3C master controller device. A local process may be able to read exposed sysfs attributes, but the UAF window depends on the controller being detached or torn down while sysfs state is still reachable.

The complete trigger is not proven to be ordinary unprivileged. Device unbind/removal or driver teardown commonly requires administrator action or a physical/device-management event, but the supplied evidence does not positively prove host-admin-equivalent privilege is required for all practical cases. Therefore HostAdminRequired is UNKNOWN rather than YES.

NamespaceScopedPrivilege is NO. No evidence suggests the I3C master controller teardown or sysfs device lifecycle is controlled through attacker-created namespaces.

Prior host setup may exist in practice because the system must have an I3C master controller and the driver/sysfs device must be present. No network exposure is indicated. Race repeatability is limited by teardown timing, but an attacker who can repeatedly trigger teardown would have more control than is established here.

4. Primitive and severity interpretation

The exact primitive is a real use-after-free of master->this. The stale object is an active structured kernel object, struct i3c_dev_desc, referenced by the master controller and consumed by sysfs callbacks after normal detach freed it too early.

This is not fixed async DMA storage. It is also not a demonstrated repeated release/refcount case. The stale operation shown is ordinary post-lifetime dereference from sysfs, not a second lifetime mutation through the same dangling reference.

PrimitiveClass is CLASS_B because a real kernel lifetime violation exists. It is constrained because the demonstrated consequence is crash/DoS, the vulnerable window is teardown-related, and no controlled reclaim, arbitrary read/write, callback control, privilege escalation, or boundary bypass is shown.

ImportantCandidate is NO because meaningful exploitation leverage beyond crash is not established. AutoDowngradeAllowed is YES because this looks like a constrained teardown/sysfs UAF without concrete repeated lifetime mutation or proven post-reuse exploitation surface. Operational severity is borderline Moderate with manual review recommended.

5. One-sentence report phrase

A use-after-free in the I3C master controller sysfs path can occur when master->this is freed during device detach before the master device and its sysfs callbacks are fully torn down, allowing a local sysfs access during teardown to dereference stale kernel memory and potentially crash the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: real kernel UAF is established, but available evidence supports mainly a teardown-time local DoS and does not establish controlled reclaim, repeated refcount mutation, or privilege-escalation leverage.

7. Call-site confidence

Call-site confidence: medium

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

Patch: i3c: master: Fix use-after-free of master->this [ Upstream
Commit: 4f3145db05fede36b35f8249b8acde5bd5d54864
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f3145db05fede36b35f8249b8acde5bd5d54864

Changed files:
  drivers/i3c/master.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=4f3145db05fede36b35f8249b8acde5bd5d54864

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

The original Linux kernel CVE announcement for CVE-2026-93200 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93200

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: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).