[CVE-2026-90337][MODERATE REGULAR] serial: core: do fallible allocations before the console can be registered [ Upstream

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

CVE: CVE-2026-90337
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: serial: core: do fallible allocations before the console can be registered [ Upstream
Commit: c2aec15f78b2e6ccd9b94216a901248511355982
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c2aec15f78b2e6ccd9b94216a901248511355982
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90337
Analysis date: Thu, 17 Sep 2026 20:09:06 -0400
ActionableScore: 2
ActionableScore lower bound: 1
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-2026-90337 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90337

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 REGULAR
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-2026-90337	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90337 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:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;**CWE-476;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'serial_core_add_one_port performed fallible allocations after the uart port was linked and after uart_configure_port could register a console. If allocation failed during driver bind, the unwind path could leave the console registered or leave state uart_port linked to a port that was being freed. This produced a NULL pointer dereference in PL011 console output and a KASAN use-after-free in i.MX console output after failed binds. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over serial driver bind or probe paths and allocation failure timing. The issue is not network reachable and is triggered locally through device or driver control paths. Impact is at least local denial of service via kernel crash. In the paranoid score it may allow confidentiality or integrity impact because the patch context shows a real use-after-free in a console output path, so manual review is needed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	NULLPTR INIT PRINTF-TTY NOMEMCHK UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Conservative signals:

* +2 Real UAF / lifetime violation. The commit explicitly reports a KASAN use-after-free in i.MX console output and a stale `state->uart_port` / registered console relationship after failed bind.
* +1 Reliable kernel crash / strong DoS. The supplied evidence reports a NULL dereference in PL011 console output and KASAN UAF after failed binds.
* -2 Host-admin-equivalent trigger. Reliable triggering appears to require serial driver bind/probe control and allocation-failure timing, which is host device-management territory.

Paranoid additional signal:

* +1 Weak structured stale-object concern. The stale object is not merely a fixed buffer. A freed or unwound `uart_port` can remain reachable through console/state paths and later be consumed by console output. This is still not enough for Class A.

Non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary read/write not demonstrated.
* Concrete repeated release/refcount mutation not established.
* Structured stale-object exploitation leverage not awarded because attacker-shaped replacement or meaningful field control is not shown.
* Extra availability not awarded because the same crash is already counted.
* C/I impact not awarded conservatively because no disclosure, overwrite, callback control, or privilege-escalation primitive is established.
* Remote reachability not established.
* Namespace-scoped privilege not established.

Repeated release/refcount check:

* First release can end lifetime: not directly established as a repeated-release sequence.
* Exact same reference survives: stale reference survives, but as console/state pointer use, not as a proven second put/free.
* Second lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount: not awarded.
* Paranoid repeated-refcount leverage: not awarded.
* FLOOR 5: not applied.

3. Reachability analysis

The vulnerable path is in `serial_core_add_one_port()` during serial port registration. The failure requires fallible allocation after the port is linked or after `uart_configure_port()` may register the console. Practical attacker control normally requires host-level control over driver binding/probing or a comparable device-management path, plus the ability to hit allocation failure timing. There is no evidence that an ordinary local user can trigger the full sequence. There is no evidence that the complete trigger is namespace-scoped. No network trigger is indicated. Special serial hardware or platform drivers such as PL011 or i.MX are involved, but the score is reduced because of host-admin reachability rather than because the hardware is rare.

4. Primitive and severity interpretation

The exact primitive is a real lifetime bug: a console or driver state can retain a reference to a `uart_port` that is being unwound or freed after a late allocation failure. This is an active structured object UAF rather than a passive resource leak. The demonstrated consequence is kernel crash / DoS through NULL dereference or KASAN-detected UAF in console output. The patch-supported practical evidence does not establish controlled reclaim, attacker-controlled replacement contents, arbitrary kernel read/write, callback hijack, or local privilege escalation.

PrimitiveClass is CLASS_B because a real kernel lifetime violation exists. ImportantCandidate is NO because the reachable model appears host-admin-equivalent and the demonstrated behavior remains crash-focused without a concrete exploitation primitive beyond stale structured use. AutoDowngradeAllowed is YES because this is a constrained, privilege-gated driver registration failure path with no repeated lifetime mutation or boundary bypass shown.

5. One-sentence report phrase

A late allocation failure in `serial_core_add_one_port()` could leave a serial console or `state->uart_port` referencing an unwound or freed port, causing NULL dereference or KASAN use-after-free in console output after failed driver binds.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: a real UAF is reported, but current evidence supports host-admin-gated crash/DoS rather than Important-class exploitation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: serial: core: do fallible allocations before the console can be registered [ Upstream
Commit: c2aec15f78b2e6ccd9b94216a901248511355982
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c2aec15f78b2e6ccd9b94216a901248511355982

Changed files:
  drivers/tty/serial/serial_core.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=c2aec15f78b2e6ccd9b94216a901248511355982

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

The original Linux kernel CVE announcement for CVE-2026-90337 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90337

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 1
  Paranoid ActionableScore: 2

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).