[CVE-2026-93097][LOW] cxl/mbox: Break poison list loop on an empty payload [ Upstream

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

CVE: CVE-2026-93097
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: cxl/mbox: Break poison list loop on an empty payload [ Upstream
Commit: 86771c105293ca26bfcc320b4f60d32c137b54aa
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86771c105293ca26bfcc320b4f60d32c137b54aa
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93097
Analysis date: Fri, 18 Sep 2026 07:45:30 -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-2026-93097 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93097

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-2026-93097	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93097 CHECK WITH IMPACT FROM ORIG NN LOW	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-835;**CWE-400;CWE-674;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A malformed or malicious CXL device can return an empty poison list payload with CXL_POISON_FLAG_MORE set, causing cxl_mem_get_poison to loop without advancing the record counter. The loop runs while holding poison.mutex, so the sysfs triggered scan thread can hang and later poison operations for the same device can be blocked. For the CVSS the PR:L reflects a conservative case where a reduced capability administrator or delegated CXL management service can trigger the sysfs scan, while normal deployments usually require root. The issue is not network reachable and requires local management access plus a malfunctioning or attacker controlled CXL device. Impact is denial of service for CXL poison handling, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
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:

* +1 Firmware-mediated external influence. The problematic input comes from a malfunctioning or malicious CXL device returning count == 0 together with CXL_POISON_FLAG_MORE.
* +1 Availability impact realistic. The loop can run forever while holding poison.mutex, hanging the sysfs-triggered poison scan thread and blocking later poison operations for that device.

Negative or non-awarded signals:

* No RealUAF. The patch does not show stale object use, post-lifetime access, double release, refcount misuse, or RCU lifetime mismatch.
* No memory corruption primitive. There is no OOB access, arbitrary write, controlled overwrite, type confusion, or active object lifetime corruption.
* No confidentiality or integrity signal. The effect is a stuck loop and blocked poison operations, not disclosure or unauthorized modification.
* No direct remote reachability. The trigger is device or firmware mediated and sysfs scan mediated, not network packet driven.
* No extra Availability point. The same mutex-held infinite loop is already counted as the availability impact.
* No resource leak signal. The bug is an infinite loop with a held mutex, not a persistent missing put or unrecoverable leaked reference.
* No Important-grade primitive. This is DoS behavior without security-boundary bypass or exploitation leverage beyond the device-local poison handling wedge.

3. Reachability analysis

The vulnerable path is cxl_mem_get_poison(), reached by a CXL poison list scan. The commit describes this as sysfs-triggered, so a local management operation is involved. The exact sysfs permission model is not visible in the supplied patch, therefore HostAdminRequired is UNKNOWN rather than YES. In normal deployments this operation is likely restricted to root or a device-management service, but that is not proven from the supplied evidence.

A malicious or malfunctioning CXL device is a material prerequisite because the device must repeatedly return an empty poison payload with the MORE flag set. This is firmware or device mediated influence, not direct remote reachability. The operation is not namespace-scoped because CXL hardware sysfs management is not a network namespace or user namespace local facility. Prior hardware presence is required: a CXL memory device supporting poison list operations must exist. No race or difficult timing is required.

4. Primitive and severity interpretation

The exact primitive is an infinite loop in the CXL poison list retrieval path when count remains zero while CXL_POISON_FLAG_MORE remains set. Because nr_records never advances, the existing max_errors guard does not terminate the loop. The loop holds poison.mutex, so the scan thread can hang and later poison operations on the same device can be blocked.

This is Class C: demonstrated DoS or invalid-state behavior without an independently useful corruption primitive. It is not active structured object UAF and not fixed stale storage UAF. There is no concrete repeated release or refcount mutation. The demonstrated consequence is local or device-mediated denial of service for CXL poison handling. A broader host compromise, privilege escalation, information leak, or integrity impact is not supported by the patch.

ImportantCandidate is NO because the issue lacks kernel memory corruption, ownership violation, authorization bypass, controlled corruption, or unresolved lifetime primitive. AutoDowngradeAllowed is YES because the established behavior is constrained DoS/resource wedging and no meaningful exploitation leverage would be lost by treating it as ordinary Moderate or Low-like.

5. One-sentence report phrase

A malformed or malicious CXL device can return an empty poison list payload with CXL_POISON_FLAG_MORE set, causing cxl_mem_get_poison() to loop while holding poison.mutex and block later poison operations on the same device.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch establishes a device-mediated infinite loop and mutex-held DoS only, with no UAF, memory corruption, authorization bypass, confidentiality impact, integrity impact, or plausible privilege escalation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: cxl/mbox: Break poison list loop on an empty payload [ Upstream
Commit: 86771c105293ca26bfcc320b4f60d32c137b54aa
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86771c105293ca26bfcc320b4f60d32c137b54aa

Changed files:
  drivers/cxl/core/mbox.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=86771c105293ca26bfcc320b4f60d32c137b54aa

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

The original Linux kernel CVE announcement for CVE-2026-93097 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93097

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: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: 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: 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).