[CVE-2026-93054][MODERATE 7.0] uio: Fix stale info pointer in failed registration path [ Upstream

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

CVE: CVE-2026-93054
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: uio: Fix stale info pointer in failed registration path [ Upstream
Commit: 63eaa7663335d482a8825c231213e312cacea567
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63eaa7663335d482a8825c231213e312cacea567
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93054
Analysis date: Fri, 18 Sep 2026 05:47:01 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93054 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93054

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-2026-93054	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93054 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-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the UIO failed registration path can leave idev info pointing to caller owned struct uio_info after /dev/uioX has already become visible to userspace. If a local process opens the device during this narrow window and registration later fails, the caller may free struct uio_info while the open file still holds a reference to the uio_device. Later file operations can dereference the stale idev info pointer, creating a use-after-free condition. For the CVSS the PR:L is used because a local user or process must be able to open /dev/uioX during the failed registration window. The issue is not network reachable. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use-after-free of driver controlled state and callbacks.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	LOCK DANGER RACE UAF HARDWARE LINUS KPANIC 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

Conservative arithmetic: +2 real UAF, +1 realistic kernel crash, -1 narrow race timing = 2. Applied REAL UAF FLOOR 4 because a real stale post-lifetime object is dereferenced and host-admin-equivalent reachability is not positively established.

Paranoid arithmetic: +2 real UAF, +1 realistic kernel crash = 3. The narrow-race penalty is withheld in the paranoid interpretation because repeated registration attempts may be possible in some deployments, but ordinary unprivileged reachability is still not fully proven. Applied REAL UAF FLOOR 5 because the stale pointer is an active structured UIO object reachable from already-open file descriptors and later file operations may consume driver-owned state after the caller frees it.

2. Signal breakdown

Positive signals:

* +2 Real UAF / lifetime violation: after `device_add()`, `/dev/uioX` can be opened, but a later registration failure leaves `idev->info` pointing to caller-owned `struct uio_info` that may be freed by the caller.
* +1 Reliable kernel crash / strong DoS: later file operations can follow `idev->info` and dereference freed memory, plausibly causing an Oops or kernel crash.
* Paranoid floor signal, not raw bonus: stale use is not only an immediate unregister-time cleanup dereference. An already-open UIO fd may later reach normal file operations through a stale active structured object.

Negative signals:

* -1 conservative hard timing: the opener must race the failed registration window after `device_add()` and before failed registration cleanup completes.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary kernel read or write is not demonstrated.
* Concrete callback hijack is not demonstrated.
* Remote reachability is not established.
* Confidentiality and integrity bonuses are not awarded as raw ActionableScore points because no concrete disclosure, arbitrary write, or controlled replacement primitive is shown.
* Extra Availability is not awarded because the same crash is already counted once.
* Concrete repeated release/refcount signal is not awarded.

Repeated release/refcount check:

* First release can end lifetime: not applicable to a repeated-release pattern.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, but due to active structured stale-object file-operation surface, not due to repeated release/refcount.

3. Reachability analysis

The immediate racing actor is a local process that opens `/dev/uioX` after the UIO device becomes visible to userspace. The full trigger also depends on a post-`device_add()` registration failure in `__uio_register_device()`. The supplied evidence does not prove that an ordinary unprivileged user can cause the registration failure or control the registering driver, but it also does not prove that host-admin-equivalent privilege is required for the complete vulnerable scenario.

`HostAdminRequired=UNKNOWN` is therefore used. `HostAdminRequired=YES` is not justified because the input establishes a userspace opener and does not positively show that only host root can participate in the complete path. `HostAdminRequired=NO` is also not justified because ordinary below-host-admin reachability for the full registration-failure sequence is not fully established.

No namespace-scoped privilege path is shown. There is no network trigger. Prior setup may involve a UIO-capable driver/device and a failing registration path. No special rare hardware requirement is proven from the patch alone. The race is narrow in the conservative interpretation because the attacker must open the device during a transient failed-registration window.

4. Primitive and severity interpretation

The exact primitive is a stale pointer / use-after-free: `idev->info` continues to point to caller-owned `struct uio_info` after the caller observes registration failure and may free that object. Already-open file descriptors keep the `uio_device` alive and can later reach `idev->info`.

This is an active structured object rather than fixed stale storage. `struct uio_info` is driver-owned UIO state used by file operations and may contain fields and operations relevant to UIO behavior. The demonstrated consequence is local denial of service through a stale dereference. The speculative consequence is stronger exploitation if reclaimed memory can be shaped or if later UIO operations consume sensitive fields in an exploitable way, but that stronger primitive is not demonstrated.

This is CLASS_B, not CLASS_A. It is stronger than CLASS_C because a real post-lifetime object use is directly established, not merely a NULL pointer or warning. It is not CLASS_A because controlled reclaim, arbitrary R/W, callback control, refcount takeover, or demonstrated LPE are not established.

ImportantCandidate=YES because the bug is a real active-object UAF reachable from an already-open userspace fd and exploitation leverage beyond crash remains unresolved. AutoDowngradeAllowed=NO because automatic closure would discard a concrete kernel lifetime primitive with meaningful unresolved exploitation surface. Operationally, this is at least Actionable Moderate and needs manual Important-vs-Moderate review.

5. One-sentence report phrase

A race in the UIO failed registration path can leave an already-open `/dev/uioX` file descriptor with access to a stale caller-owned `struct uio_info`, leading to a real use-after-free and at least local kernel crash risk, with unresolved exploitation leverage requiring manual review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: real active structured UAF is established, later userspace-driven file operations may dereference freed driver-owned state, and stronger exploitation cannot be ruled out from the patch alone.

7. Call-site confidence

Call-site confidence: medium

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

Patch: uio: Fix stale info pointer in failed registration path [ Upstream
Commit: 63eaa7663335d482a8825c231213e312cacea567
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63eaa7663335d482a8825c231213e312cacea567

Changed files:
  drivers/uio/uio.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=63eaa7663335d482a8825c231213e312cacea567

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

The original Linux kernel CVE announcement for CVE-2026-93054 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93054

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: 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).