[CVE-2026-90216][LOW] ubi: Fix rollback for explicit UBI device numbers [ Upstream

[CVE-2026-90216][LOW] ubi: Fix rollback for explicit UBI device numbers [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90216
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ubi: Fix rollback for explicit UBI device numbers [ Upstream
Commit: 83c978921688af40dcab6db74882d1ff9b0b765c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=83c978921688af40dcab6db74882d1ff9b0b765c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90216
Analysis date: Thu, 17 Sep 2026 18:19:14 -0400
ActionableScore: 0
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-2026-90216 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90216

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-2026-90216	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90216 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:H/UI:N/S:U/C:N/I:N/A:H';CWE-404;*CWE-772;CWE-755;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'UBI rollback during ubi_init_attach can miss already attached devices when mtd parameters use explicit UBI device numbers. A later initialization failure may leave a UBI device attached at a higher ubi_devices slot because rollback scanned only by parameter index rather than actual device index. For the CVSS the PR:H is used because reliable triggering requires control over UBI module initialization, MTD command line parameters, or boot configuration. The issue is not network reachable and does not indicate memory corruption, information disclosure, or privilege escalation. Impact is denial of service or resource retention only, such as leaked device state or blocked reuse of the affected MTD/UBI resources.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	SIMPLEFIX HARDWARE DEBUGFS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: -1
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Floor/cap: raw conservative score was clamped from -1 to 0. No UAF floor applies. No Important preservation floor applies.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak: rollback can miss an already attached UBI device stored at a higher ubi_devices slot when explicit ubi_num is used.
* +1 Paranoid availability/resource-retention concern: a missed detach may leave UBI/MTD state attached after initialization failure and could block reuse or cleanup of affected resources.

Negative signals:

* -2 Host-admin-equivalent prerequisite: reliable triggering requires control over UBI initialization, module or boot parameters, or MTD/UBI device setup.

Non-awarded signals:

* RealUAF not awarded: no stale post-free object use is established.
* Concrete repeated release/refcount not awarded: the patch fixes a missed detach, not a second put/release/free on the same dangling reference.
* Memory corruption not awarded: no OOB, UAF, double free, arbitrary write, or type confusion is shown.
* Reliable kernel crash not awarded: the supplied evidence describes missed rollback/resource retention, not a demonstrated panic.
* C/I impact not awarded: no information disclosure, unauthorized data modification, or privilege escalation primitive is established.
* Remote reachability not awarded: no network path exists.
* Manual-review preservation not awarded: this is privileged rollback cleanup logic without a concrete corruption or security-boundary primitive.

3. Reachability analysis

The vulnerable path is in ubi_init_attach(), which runs during UBI initialization and rollback after module/init failure. The relevant inputs are mtd= parameters and explicit UBI device numbers. Reliable triggering requires control over boot/module configuration or MTD/UBI device initialization, which is host-admin-equivalent in normal systems.

Ordinary local users cannot normally configure this path. No namespace-scoped capability path is established. No network trigger is present. No special race is required. The issue depends on UBI/MTD being used and explicit ubi_num being configured, but the main reducing factor is host-admin control rather than subsystem rarity.

4. Primitive and severity interpretation

The exact primitive is a cleanup/rollback mismatch: rollback scans by mtd parameter index while devices are stored by actual UBI device number. This can miss a previously attached device and leave resources behind after a later initialization failure.

This is not an active structured UAF and not fixed stale storage. It is a resource/reference cleanup bug. There is no concrete repeated release/refcount operation. The demonstrated consequence is resource retention or possible local DoS of affected UBI/MTD resources. Stronger consequences such as memory corruption, privilege escalation, or confidentiality/integrity impact are not supported.

PrimitiveClass=NONE because no meaningful kernel corruption, ownership violation, authorization bypass, or lifetime-after-free primitive is established. ImportantCandidate=NO because the issue is host-admin-gated cleanup logic with only resource-retention impact. AutoDowngradeAllowed=YES because no unresolved Important-grade primitive would be lost.

5. One-sentence report phrase

UBI rollback can miss attached devices when explicit ubi_num values place them outside the scanned parameter-index range, leaving resources attached after initialization failure, but exploitation requires host-admin-level UBI or boot configuration control and no memory corruption or privilege escalation is established.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a privileged initialization rollback/resource-retention issue with no UAF, no repeated lifetime mutation, no network exposure, and no authorization or ownership boundary bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: ubi: Fix rollback for explicit UBI device numbers [ Upstream
Commit: 83c978921688af40dcab6db74882d1ff9b0b765c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=83c978921688af40dcab6db74882d1ff9b0b765c

Changed files:
  drivers/mtd/ubi/build.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=83c978921688af40dcab6db74882d1ff9b0b765c

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

The original Linux kernel CVE announcement for CVE-2026-90216 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90216

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: 0

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).