[CVE-2026-89588][MODERATE REGULAR] ACPI: APEI: GHES: fix ARM section length accounting after header

[CVE-2026-89588][MODERATE REGULAR] ACPI: APEI: GHES: fix ARM section length accounting after header

[AL-KERNEL]

CVE: CVE-2026-89588
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ACPI: APEI: GHES: fix ARM section length accounting after header
Commit: 5ff385e9403e87ae33f65b8c38698d3b1e92cfde
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ff385e9403e87ae33f65b8c38698d3b1e92cfde
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89588
Analysis date: Sat, 12 Sep 2026 05:19:54 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
An incorrect `sizeof` use in the ACPI APEI GHES ARM CPER parser can overestimate the remaining section length and allow an out-of-bounds read, potentially causing a kernel crash when malformed firmware-supplied error records are processed.

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

The original Linux kernel CVE announcement for CVE-2026-89588 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89588

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-89588	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89588 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H';CWE-467;CWE-125;CWE-130;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '5.1';DESCR 'An out of bounds read can occur in the ACPI APEI GHES ARM error parser because ghes_handle_arm_hw_error advances past the cper_sec_proc_arm header but subtracts sizeof pointer instead of sizeof structure from the remaining section length. This can make the parser believe that more bytes are available for cper_arm_err_info records than the CPER section actually contains when err_info_num is large enough. For the CVSS the PR:H is used because reliable triggering normally requires privileged firmware error injection or control over platform supplied CPER records. The issue is not directly network reachable and is tied to local platform firmware or RAS error reporting paths. Impact is mainly kernel out of bounds read with possible information exposure or denial of service if the read crosses invalid memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-89588 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	SIMPLEFIX 	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap changed the score.
* Final recommended bucket: **Borderline / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* +1 Weak OOB read / invalid read candidate. The parser advances by `sizeof(*err)` but previously subtracted only `sizeof(err)`, so the remaining CPER section length could be overestimated.
* +1 Potential kernel DoS. If `err_info_num` is large enough relative to `error_data_length`, the parser can read past the CPER ARM section and may fault or destabilize the kernel parser path.

Paranoid additional signal:

* +1 Firmware-mediated external influence. CPER/GHES data is platform supplied, so a malformed record could matter if an attacker can influence firmware, hardware error reporting, or privileged error injection. This is not direct network reachability.

Non-awarded signals:

* No UAF or lifetime violation is established.
* No OOB write is established.
* No arbitrary write or controlled corruption is established.
* No controlled disclosure path is shown, so confidentiality is not awarded merely because an internal OOB read exists.
* No integrity impact is established.
* No direct remote reachability is established.
* No privilege escalation primitive is established.
* No repeated release/refcount mutation exists.
* No extra Availability point is awarded beyond the same possible parser fault.

## 3. Reachability analysis

The vulnerable input is an ARM CPER section processed by ACPI APEI GHES. The realistic trigger depends on platform firmware, hardware error reporting, or error injection facilities.

Host-admin-equivalent privilege is not proven from the supplied patch alone, but below-host-admin reachability is also not proven. Therefore `HostAdminRequired=UNKNOWN`.

Namespace-scoped privilege does not apply. There is no evidence that user, network, or container namespaces provide the complete trigger chain.

This is not directly network reachable. It is firmware/RAS-path mediated. A privileged local actor with access to error injection, or a compromised or malicious firmware/error source, is the more plausible attacker model.

No special race is involved. The bug is deterministic length-accounting logic once a malformed CPER ARM section is processed.

## 4. Primitive and severity interpretation

The exact primitive is an out-of-bounds read in the ACPI APEI GHES ARM CPER parser caused by subtracting pointer size instead of structure size after advancing past the header.

This is not active structured-object UAF and not fixed stale storage. It is a parser bounds/accounting bug.

Primitive class is `CLASS_C` because the demonstrated behavior is an invalid/OOB read with possible crash or parser fault, but without an independently useful corruption, disclosure, authorization-bypass, or privilege-escalation primitive.

The demonstrated consequence is potential DoS or invalid kernel read while parsing malformed firmware-supplied records. A speculative consequence is limited information exposure if out-of-section bytes are later exposed through logs or reports, but that disclosure path is not established by the supplied evidence.

`ImportantCandidate=NO` because there is no UAF, write primitive, controlled corruption, boundary bypass, or demonstrated LPE. `AutoDowngradeAllowed=YES` because the issue is a constrained OOB read/parser bounds bug with no unresolved Important-grade primitive, although manual review is still recommended due to kernel parser and firmware-supplied input.

Likely operational severity: ordinary to borderline Moderate, not Important-class on the supplied evidence.

## 5. One-sentence report phrase

An incorrect `sizeof` use in the ACPI APEI GHES ARM CPER parser can overestimate the remaining section length and allow an out-of-bounds read, potentially causing a kernel crash when malformed firmware-supplied error records are processed.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: kernel OOB read in firmware/RAS parsing is real, but the supplied evidence does not establish direct attacker reachability, disclosure, write corruption, UAF, or privilege escalation.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: ACPI: APEI: GHES: fix ARM section length accounting after header
Commit: 5ff385e9403e87ae33f65b8c38698d3b1e92cfde
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ff385e9403e87ae33f65b8c38698d3b1e92cfde

Commit description:

In ghes_handle_arm_hw_error(), after skipping the cper_sec_proc_arm
header with (err + 1), the remaining length was reduced by sizeof(err)
(pointer size) instead of sizeof(*err) (structure size).

That overestimates the bytes left for cper_arm_err_info records and can
let the parser read past the CPER section when err_info_num is large
enough relative to error_data_length.

Use sizeof(*err) so the length accounting matches the pointer advance
and the earlier sizeof(*err) size check.

Fixes: 87880af ("APEI/GHES: ARM processor Error: don't go past allocated memory")
Cc: stable@vger.kernel.org
Signed-off-by: TanZheng <tanzheng@kylinos.cn>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Link: https://patch.msgid.link/20260806010944.32384-1-kensanya@163.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/acpi/apei/ghes.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=5ff385e9403e87ae33f65b8c38698d3b1e92cfde

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

The original Linux kernel CVE announcement for CVE-2026-89588 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89588

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:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.1

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: 2
  Paranoid ActionableScore: 3

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).