[CVE-2026-90070][LOW] tpm: st33zp24: Return zero on status read failure [ Upstream

[CVE-2026-90070][LOW] tpm: st33zp24: Return zero on status read failure [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90070
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: tpm: st33zp24: Return zero on status read failure [ Upstream
Commit: d732cfc4befe28f02ec82ed5fd2bc2a21fbabd42
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d732cfc4befe28f02ec82ed5fd2bc2a21fbabd42
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90070
Analysis date: Fri, 18 Sep 2026 01:06:07 -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-2026-90070 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90070

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-2026-90070	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90070 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';*CWE-457;CWE-252;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.6';DESCR 'st33zp24_status can return an uninitialized stack byte as TPM_STS flags when the transport recv callback fails or returns less than one byte. This can make TPM status checks complete spuriously and may cause incorrect retry timeout or error handling in TPM command processing. For the CVSS the PR:L is used because a local user or local process with access to the TPM device interface is the realistic trigger context, while reliable exploitation also depends on a transport read failure or short read. The issue is not network reachable. Impact is mainly local denial of service or low integrity impact for TPM operations, with no supported evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	SIMPLEFIX ERRORPATH IMPROVEONLY LINUS 	NO	NO	checked

======================================================================
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 was applied.

2. Signal breakdown

Conservative positive signals:

* +1 Weak invalid-state / bogus structured-status interpretation: `st33zp24_status()` may return an uninitialized stack byte as `TPM_STS` flags when the transport `recv()` fails or returns fewer than one byte.

Paranoid additional signals:

* +1 Limited device-operation availability / integrity concern: a bogus TPM status value may cause status checks to complete spuriously and may send callers into incorrect retry, timeout, completion, or error behavior for TPM operations.

Non-awarded material signals:

* +0 Real UAF not awarded: no freed object, stale lifetime use, double release, RCU lifetime mismatch, or refcount corruption is established.
* +0 Memory corruption not awarded: the bug is an uninitialized local byte consumed internally as status flags, not an overwrite, UAF, OOB access, or controlled type confusion.
* +0 Confidentiality not awarded: no path shows the uninitialized stack byte being disclosed to userspace, network, device-visible output, or another security principal.
* +0 Strong integrity not awarded: no unauthorized modification of protected kernel state, credentials, files, or policy is established.
* +0 Reliable kernel crash not awarded: the patch and description support spurious TPM status handling, not a kernel panic or host-wide fatal fault.
* +0 Remote reachability not awarded: this is a local TPM driver path, not a network-exposed parser.
* +0 Strong semantic reinterpretation not awarded: although a stack byte is interpreted as `TPM_STS`, the value is not shown to control active pointers, ownership, descriptors, callbacks, or memory access.
* +0 Manual-review preservation signals not awarded: no authorization bypass, shared-page ownership violation, KVM boundary issue, repeated release/refcount mutation, or active structured UAF is present.

Negative signals:

* No negative privilege penalty applied. Host-admin-equivalent privilege is not positively established, but complete below-host-admin triggerability is also not fully established.
* No hardware rarity penalty applied. The code is hardware-specific, but the supplied evidence does not prove rare or physical-only attacker prerequisites beyond use of this TPM driver.

3. Reachability analysis

The vulnerable path is the status callback for the STMicroelectronics `st33zp24` TPM driver. A local process that can cause TPM commands or status polling may reach the status-read path, but reliable manifestation depends on the transport `recv()` failing or returning a short read. The supplied evidence mentions I2C transport behavior where `i2c_master_recv()` may be skipped after a short or failed register-select write, leaving the stack byte uninitialized.

Host-admin-equivalent privilege is not proven as a strict requirement. However, ordinary unprivileged reachability is also not fully proven because TPM device access is commonly policy-controlled by device permissions, system services, or a TPM resource manager. Therefore `HostAdminRequired=UNKNOWN`.

No namespace-scoped privilege model is relevant. The complete trigger is not shown to be performable inside an attacker-created namespace. `NamespaceScopedPrivilege=NO`.

There is no network reachability. There is no race. There is no evidence of attacker-controlled kernel memory layout, reclaim, object lifetime manipulation, or repeated lifetime transition. A real system must have the affected TPM driver and a transport failure or short-read condition.

4. Primitive and severity interpretation

The exact primitive is an unchecked transport-read result causing an uninitialized stack byte to be interpreted as TPM status flags. This is an internal invalid-state primitive, not a memory-corruption primitive. It is not active structured stale storage, not fixed stale storage, and not a UAF.

The demonstrated consequence is spurious status completion or incorrect TPM command state handling. The practical impact is low: local TPM operation disruption, incorrect retry or timeout behavior, or limited TPM command integrity concern. No kernel crash, information disclosure, privilege escalation, or security-boundary bypass is supported.

Primitive class is `CLASS_C` because the behavior is primarily invalid-state / DoS-like and does not establish an independently useful corruption or authorization primitive.

`ImportantCandidate=NO` because there is no concrete kernel corruption, no real lifetime violation, no authorization bypass, no protected-resource access, and no plausible path to LPE supported by the patch.

`AutoDowngradeAllowed=YES` because the issue is low-impact and does not leave unresolved exploitation leverage that would be lost by automatic downgrade.

Likely operational severity: ordinary Low / Moderate-like TPM driver correctness issue.

5. One-sentence report phrase

An unchecked status read in the st33zp24 TPM driver can return an uninitialized stack byte as TPM_STS flags after a transport read failure, causing spurious TPM status completion or local TPM operation disruption without evidence of kernel memory corruption, information disclosure, or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch establishes an internal uninitialized-status-byte bug with low operational impact and no UAF, overwrite, disclosure path, authorization bypass, or LPE-relevant primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: tpm: st33zp24: Return zero on status read failure [ Upstream
Commit: d732cfc4befe28f02ec82ed5fd2bc2a21fbabd42
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d732cfc4befe28f02ec82ed5fd2bc2a21fbabd42

Changed files:
  drivers/char/tpm/st33zp24/st33zp24.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=d732cfc4befe28f02ec82ed5fd2bc2a21fbabd42

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

The original Linux kernel CVE announcement for CVE-2026-90070 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90070

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:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS score: 3.6

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).