[CVE-2026-90323][LOW] ublk: validate auto buf reg before taking uring_cmd [ Upstream

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

CVE: CVE-2026-90323
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ublk: validate auto buf reg before taking uring_cmd [ Upstream
Commit: 653d22269a8b83b491f7f186a5d7872f14e6ddca
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=653d22269a8b83b491f7f186a5d7872f14e6ddca
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90323
Analysis date: Thu, 17 Sep 2026 18:35:49 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90323 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90323

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-2026-90323	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90323 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-754;*CWE-664;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'An ordering flaw in the ublk automatic buffer registration path allows an invalid sqe address to be rejected only after ublk_fill_io_cmd() has marked the tag active and associated it with an io_uring command. The command can then be completed while its tag remains active, causing ublk device teardown to wait indefinitely and producing a local denial of service. A related ordering issue in the FETCH path can modify the stored buffer state before the command state checks succeed. For the CVSS the PR:L value is selected because triggering requires a local process with access to the ublk command interface, but this process may be an unprivileged or reduced capability ublk server rather than a fully privileged administrator. The issue is not directly network reachable. The demonstrated impact is a teardown hang without evidence of a UAF, out of bounds access, information disclosure, or arbitrary write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)  SKIP CVE-2026-90323 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	INIT IMPROVEONLY IO_URING  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Availability impact realistic. An invalid automatic buffer registration descriptor can leave a tag active after its uring command is completed, causing ublk device teardown to wait indefinitely.
* +0 Local unprivileged trigger. A local ublk server can submit the command, but the supplied evidence does not establish that an ordinary user can create and operate the complete vulnerable configuration without prior delegation or privileged setup.
* +0 Memory corruption. No UAF, OOB access, stale dereference, double release, arbitrary write, or controlled corruption is established.
* +0 Strong host-wide DoS. The demonstrated effect is a ublk teardown hang rather than a kernel panic or proven host-wide failure.
* +0 Additional availability. The same teardown hang is not counted twice.
* +0 Confidentiality and integrity. No disclosure, unauthorized modification, or security-boundary bypass is demonstrated.
* +0 Race penalty. This is an ordered validation and state-transition flaw, not a timing race.
* +0 Resource leak. An active tag is left behind, but the evidence primarily establishes a stuck teardown rather than an accumulating persistent kernel allocation or reference leak.
* Controlled reclaim, arbitrary write, privilege escalation, remote reachability, and exploitation leverage beyond denial of service are not demonstrated.
* No repeated release or refcount operation exists. There is no first lifetime-ending release, surviving dangling reference, or second lifetime mutation. The repeated-release signal and UAF floors do not apply.

3. Reachability analysis

The trigger is local and requires a process with access to the relevant ublk command interface to submit an invalid automatic buffer registration value through io_uring. Such a process may be a dedicated or delegated ublk server, but the supplied material does not conclusively establish whether the complete setup is available to an ordinary unprivileged user or requires prior host administration. Therefore, `HostAdminRequired` remains `UNKNOWN`, and neither an unprivileged-trigger bonus nor a privilege penalty is applied.

No network trigger is present. No namespace-scoped capability chain is involved. No special hardware or timing race is required. `UBLK_F_AUTO_BUF_REG` must be enabled for the affected device.

4. Primitive and severity interpretation

The exact primitive is an invalid state transition. `ublk_fill_io_cmd()` marks a tag active before the automatic buffer descriptor is validated. Validation failure then completes the uring command without clearing the active tag, allowing teardown to wait indefinitely. The FETCH path also writes buffer state before completing its command-state checks.

This is `CLASS_C` invalid-state and denial-of-service behavior. It is not a demonstrated lifetime violation because the patch does not show later dereferencing, freeing, or refcount mutation through the completed uring command. The practical consequence is a device teardown hang. Stronger consequences such as kernel memory corruption, host-wide panic, information disclosure, or privilege escalation are unsupported.

`ImportantCandidate=NO` because there is no unresolved corruption or security-boundary primitive. `AutoDowngradeAllowed=YES` because the demonstrated behavior is constrained local DoS without useful post-failure exploitation leverage.

5. One-sentence report phrase

An ordering flaw in ublk automatic buffer registration can complete an invalid io_uring command while leaving its tag active, causing local ublk device teardown to hang without demonstrated memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a local state-management DoS with no UAF, repeated lifetime mutation, security-boundary bypass, or unresolved corruption primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: ublk: validate auto buf reg before taking uring_cmd [ Upstream
Commit: 653d22269a8b83b491f7f186a5d7872f14e6ddca
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=653d22269a8b83b491f7f186a5d7872f14e6ddca

Changed files:
  drivers/block/ublk_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=653d22269a8b83b491f7f186a5d7872f14e6ddca

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

The original Linux kernel CVE announcement for CVE-2026-90323 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90323

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 1

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).