[CVE-2026-89439][LOW] platform/x86: ISST: Add a NULL check for sst_inst[]

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

CVE: CVE-2026-89439
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: platform/x86: ISST: Add a NULL check for sst_inst[]
Commit: 49a95fe1f64f41c2e8959e525aefdb10f23b293e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49a95fe1f64f41c2e8959e525aefdb10f23b293e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89439
Analysis date: Sat, 12 Sep 2026 03:14:20 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A local NULL pointer dereference in the Intel ISST TPMI ioctl path can occur when socket loading failed and `isst_common.sst_inst(socket_id)` is NULL, causing denial of service through a kernel crash without evidence of UAF, information disclosure, integrity impact, or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-89439 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89439

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89439	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89439 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-476;CWE-754;CWE-703;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'An ISST TPMI ioctl path can dereference a NULL sst_inst pointer in isst_if_get_tpmi_instance_count when socket loading failed but the user requests the instance count for that socket. This can cause a local kernel crash through the platform x86 Intel Speed Select interface, resulting in denial of service. For the CVSS the PR:L is used for the paranoid score because a local process with access to the ISST interface can issue the request, while typical deployments may restrict the device to administrative users. The issue is not network reachable. Impact is denial of service only, with no indication of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	SIMPLEFIX IMPROVEONLY  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=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: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

## 2. Signal breakdown

Conservative signals:

* +1 Reliable kernel crash / strong DoS: `sst_inst` can be NULL after failed socket loading, and the old code passes it to `isst_instance_count()`, plausibly causing a local NULL pointer dereference.
* +0 Local unprivileged trigger: not awarded because ordinary unprivileged access to the ISST TPMI ioctl interface is not established.
* +0 C/I impact: no evidence of information disclosure, unauthorized write, UAF, OOB access, type confusion, or privilege escalation.
* +0 Remote reachability: not network reachable.
* +0 Race/timing: no race is involved.
* +0 Repeated release/refcount: no put/free/refcount mutation is involved.
* +0 Structured stale-object leverage: no stale object exists.
* +0 Resource leak: no persistent leak is established.

Paranoid additional signal:

* +1 Possible below-host-admin local reachability: supplied prior analysis suggests `PR:L` may be defensible if a local process has access to the ISST interface. This raises practical triage slightly but does not create a corruption primitive.

Negative signals:

* No host-admin penalty was applied because host-admin-equivalent privilege is not positively established from the supplied evidence.
* No rare-hardware penalty was applied. The code is hardware/platform-specific, but affected-system triage should not subtract merely because a driver requires matching hardware.

## 3. Reachability analysis

The trigger is local through the Intel Speed Select TPMI platform/x86 interface, likely an ioctl/control path reaching `isst_if_get_tpmi_instance_count()`. The attacker-controlled input appears to include a `socket_id`, which is used to index `isst_common.sst_inst[]` after earlier validation.

The complete privilege boundary is unresolved. Typical deployments may restrict access to administrative users or privileged services, but the supplied evidence does not prove host-admin-equivalent privilege is required. Therefore `HostAdminRequired=UNKNOWN`.

Namespace-scoped privilege is not applicable. This is a platform hardware management interface, not a network namespace, user namespace, or container-scoped operation. Therefore `NamespaceScopedPrivilege=NO`.

There is no network path, no packet-triggered behavior, no prior namespace setup, and no race. The vulnerable condition depends on a failed socket loading state plus a request for the affected socket instance count.

## 4. Primitive and severity interpretation

The exact primitive is a local NULL pointer dereference. `isst_common.sst_inst[tpmi_inst.socket_id]` may be NULL, and the old code did not check it before passing it to `isst_instance_count()`.

This is not an active structured UAF and not fixed stale storage. There is no post-lifetime object use, no repeated release/refcount mutation, no controlled reclaim, no arbitrary read/write, no callback control, and no security-boundary bypass.

Primitive class is `CLASS_C`: demonstrated behavior is crash/DoS/invalid-state behavior without an independently useful corruption primitive.

Demonstrated consequence is local denial of service through kernel crash or Oops. Speculative consequences beyond DoS are not supported by the patch or supplied context.

`ImportantCandidate=NO` because there is no meaningful unresolved memory-corruption, lifetime, authorization, filesystem ownership, or security-boundary primitive. `AutoDowngradeAllowed=YES` because this is a constrained NULL dereference with DoS-only impact and no unresolved exploitation leverage.

Likely operational severity is ordinary Moderate or Low-like, depending on actual device permissions in the evaluated product.

## 5. One-sentence report phrase

A local NULL pointer dereference in the Intel ISST TPMI ioctl path can occur when socket loading failed and `isst_common.sst_inst(socket_id)` is NULL, causing denial of service through a kernel crash without evidence of UAF, information disclosure, integrity impact, or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch establishes only a NULL check before dereference, with DoS-only impact and no concrete corruption, lifetime, authorization, or boundary-bypass primitive.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: platform/x86: ISST: Add a NULL check for sst_inst[]
Commit: 49a95fe1f64f41c2e8959e525aefdb10f23b293e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49a95fe1f64f41c2e8959e525aefdb10f23b293e

Commit description:

To be consistent with other places, add a NULL check for failed socket
loading by checking isst_common.sst_inst[].

Fixes: d805456 ("platform/x86: ISST: Enumerate TPMI SST and create framework")
Cc: stable@vger.kernel.org
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260811222134.3912626-3-srinivas.pandruvada@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/platform/x86/intel/speed_select_if/isst_tpmi_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=49a95fe1f64f41c2e8959e525aefdb10f23b293e

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

The original Linux kernel CVE announcement for CVE-2026-89439 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89439

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:H
  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: 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: 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).