[CVE-2026-89740][MODERATE REGULAR] serial: imx: serialize imx_uart_ports[] lifetime

[CVE-2026-89740][MODERATE REGULAR] serial: imx: serialize imx_uart_ports[] lifetime

[AL-KERNEL]

CVE: CVE-2026-89740
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: serial: imx: serialize imx_uart_ports[] lifetime
Commit: 681696ae9e4a28bdf54893c807dfe4a6c08e30a5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=681696ae9e4a28bdf54893c807dfe4a6c08e30a5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89740
Analysis date: Sat, 12 Sep 2026 05:32:16 -0400
ActionableScore: 2
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-2026-89740 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89740

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-2026-89740	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89740 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-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A dangling pointer can remain in the imx_uart_ports table because imx_uart_probe publishes a devm allocated port before uart_add_one_port() completes and the entry was not cleared on add failure or after removal. A sibling UART probe can later use the stale table entry during shared console registration, which can turn the stale pointer into a use-after-free condition observed by KASAN. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate device management or driver rebinding to a reduced capability local administrator rather than full host root. The issue is not network reachable and requires local control over the device or driver lifecycle on affected i.MX UART systems. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to a real stale pointer UAF class.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	KASAN INIT PRINTF-TTY LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

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

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +2 Real UAF / lifetime violation: `imx_uart_ports[]` can retain a dangling pointer to a devm-allocated `struct imx_port` after `uart_add_one_port()` failure or after port removal. A sibling probe can later consume the stale entry.
* +1 Reliable kernel crash / strong DoS: the issue was reproduced under KASAN, and the stale pointer use is a plausible kernel crash path.
* +1 Secondary index / registration-table staleness: the global `imx_uart_ports[]` table is a registration/lookup table that remains synchronized incorrectly with the actual UART port lifetime.

Negative signals:

* -2 Host-admin-equivalent device lifecycle control: the demonstrated trigger uses unbind/rebind of platform UART devices and console UART lifecycle manipulation, which is normally host-root or host-admin-equivalent control.

Non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded merely because UAF exists.
* Structured stale-object exploitation leverage not awarded because no attacker-shaped replacement object, callback control, or meaningful post-reuse field consumption is established.
* Weak LPE not awarded solely from the UAF class.
* Concrete repeated release/refcount signal not awarded. The patch does not show a first put/free followed by a second lifetime-mutating operation on the exact same stale reference.
* Extra availability point not awarded because the crash/KASAN consequence is already counted once.
* Race penalty not applied. The reproduced stale-entry sequence is lifecycle/order based, and the prompt does not establish a narrow externally uncontrollable timing race.

Repeated-release/refcount check:

* First release can end lifetime: not established as a visible first release/put on the same reference.
* Exact same reference survives to second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.

3. Reachability analysis

The demonstrated trigger requires local control over the affected i.MX UART device lifecycle: unbinding a sibling UART, unbinding the console UART, and rebinding the sibling. That is normally performed through privileged sysfs driver/device management and is host-admin-equivalent in ordinary Linux deployments.

No network trigger is established. No namespace-scoped privilege path is shown. The vulnerable operation is not a packet-processing or remotely reachable protocol path.

Prior setup requires an affected system with the i.MX UART driver and console-related shared table behavior. This is hardware/platform specific, but no separate hardware rarity penalty is applied because the issue is already strongly constrained by host-admin device lifecycle control.

The bug has concurrency/lifetime aspects, and the fix serializes add/remove with table updates. However, the evidence does not show a hard attacker-uncontrollable race that should receive an additional timing penalty.

4. Primitive and severity interpretation

The exact primitive is a stale global registration-table pointer to a devm-allocated active structured driver object, later consumed by sibling UART console registration. This is a real Class B lifetime/UAF issue.

The stale object is an active structured object rather than a fixed passive buffer, but the observed and supported consequence is KASAN-detected use-after-free and likely kernel crash. The patch does not establish controlled reclaim, attacker-controlled replacement contents, callback/function-pointer control, arbitrary read/write, information disclosure, or privilege escalation.

This is not an ordinary repeated-release/refcount UAF. It is closer to an active structured stale-pointer dereference through a stale registration table. The stale table entry is security-relevant for stability, but the exploitation leverage beyond crash remains weak under the supplied evidence.

ImportantCandidate=NO because the complete supported chain is host-admin-gated and crash-oriented, with no meaningful unresolved exploitation primitive such as controlled reuse, repeated lifetime mutation, or boundary bypass.

AutoDowngradeAllowed=YES because this is a constrained Class B driver lifecycle UAF where the demonstrated effect is crash/DoS, the trigger is host-admin-equivalent, and no stronger corruption or security-boundary primitive is established.

Likely operational severity: ordinary Moderate / Low-like for security triage, though still worth fixing for kernel robustness.

5. One-sentence report phrase

A stale pointer in the i.MX UART global port table can be consumed by sibling console registration after port add failure or removal, causing a KASAN-observed use-after-free and likely local kernel crash, but the demonstrated trigger requires host-admin device lifecycle control and no privilege escalation primitive is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a real UAF in a global driver registration table, so a human should confirm product-specific reachability and whether any non-host-admin device-management delegation exists. Based on supplied evidence, urgent Important-class handling is not justified.

7. Call-site confidence

Call-site confidence: high

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

Patch: serial: imx: serialize imx_uart_ports[] lifetime
Commit: 681696ae9e4a28bdf54893c807dfe4a6c08e30a5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=681696ae9e4a28bdf54893c807dfe4a6c08e30a5

Commit description:

imx_uart_probe() publishes its devm-allocated port in imx_uart_ports[]
before uart_add_one_port() because console setup uses the table. The entry
is not cleared when adding the port fails or after removal, leaving a
dangling pointer.

A sibling probe can register the shared console through that stale entry.
This was reproduced under KASAN on QEMU mcimx6ul-evk by unbinding a
sibling UART, unbinding the console UART and rebinding the sibling.

Keep the entry valid through uart_remove_one_port(), then clear it. Protect
port addition and removal together with their table updates so sibling
operations cannot interleave. Reject an occupied slot rather than
clobbering an active port during a duplicate-line probe.

Fixes: dbff4e9 ("IMX UART: remove statically initialized tables")
Fixes: 9f322ad ("imx: serial: handle initialisation failure correctly")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/all/20260719162850.043B41F000E9@smtp.kernel.org
Link: https://lore.kernel.org/all/20260719222501.CB4CB1F000E9@smtp.kernel.org
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260731181844.11330-6-kmehltretter@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/tty/serial/imx.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=681696ae9e4a28bdf54893c807dfe4a6c08e30a5

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

The original Linux kernel CVE announcement for CVE-2026-89740 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89740

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: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: 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).