[CVE-2026-68400][MODERATE 7.0] firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation [ Upstream

[CVE-2026-68400][MODERATE 7.0] firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68400
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation [ Upstream
Commit: b39b08e6bee812514b449dc874076890e6b871a0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b39b08e6bee812514b449dc874076890e6b871a0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68400
Analysis date: Mon, 10 Aug 2026 11:44:26 -0400
ActionableScore: 6
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An ARM FF-A descriptor offset bug can place Endpoint Memory Access Descriptor entries at the wrong location during memory sharing setup, causing malformed firmware-facing memory descriptors and possible local DoS or constrained descriptor corruption on FF-A v1.1 systems.

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

The original Linux kernel CVE announcement for CVE-2026-68400 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68400

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 7.0
Manual review required: YES

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
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CVE-2026-68400	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-682;CWE-131;*CWE-787;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '7';DESCR 'An offset calculation bug in the ARM FF-A memory sharing path can place Endpoint Memory Access Descriptor entries at the wrong position for FF-A v1.1 descriptors. This can produce malformed memory descriptors and may corrupt the FF-A transmit buffer layout when descriptor offsets or sizes are inconsistent with max_fragsize. For the CVSS the PR:L is used for the paranoid score because a local user may indirectly reach FF-A memory sharing through exposed kernel clients, trusted application interfaces, or delegated services, while direct low level setup is usually administrator controlled. The issue is not network reachable and requires local interaction with an ARM FF-A enabled system. Impact is at least local denial of service or memory sharing failure, and in the worst case may allow confidentiality or integrity impact due to descriptor or buffer corruption. For the paranoid score, choose the highest still-defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-68400 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX IMPROVEONLY LINUS  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid score signals:

* Firmware-mediated external influence: +1. The bug is in ARM FF-A memory sharing descriptor construction and depends on FF-A v1.1 descriptor layout consumed by firmware or secure world.
* Local trigger with possible lower privilege path: +1. Direct setup is likely kernel or privileged-client driven, but some systems may expose FF-A backed services through trusted application or delegated interfaces.
* Constrained kernel buffer overwrite or weak indirect corruption candidate: +1. The old code placed EMAD entries using `sizeof(struct ffa_mem_region)` instead of `ep_mem_offset`, and wrote descriptor fields at the calculated location.
* Memory layout invariant restoration: +1. The patch restores consistency between `ep_mem_offset`, `composite_offset`, `emad_size`, and `max_fragsize`.
* Privileged kernel or device-management corruption path: +1. The affected buffer describes memory sharing permissions and layout for a firmware-mediated trusted interface.
* Availability impact realistic: +1. Malformed descriptors can plausibly cause FF-A memory sharing failure, firmware rejection, or local service disruption.

Conservative reductions:

* Requires privileged or kernel-mediated access in typical deployments: -2. There is no evidence of a broadly exposed unprivileged syscall path.
* No direct remote reachability. No score for network-triggerable exposure.
* No strong proven LPE primitive. No score for strong privilege escalation.

## 3. Reachability analysis

The affected path is local and ARM FF-A specific. It is not network reachable. In a typical deployment, triggering requires a kernel client, a privileged service, or a driver path that performs FF-A memory share operations. Namespace or container exposure is unclear from the patch alone. A paranoid interpretation should consider systems where a reduced-privilege local process can indirectly request FF-A memory sharing through a trusted application interface or delegated device service.

Path default exposure is platform dependent. It matters mainly on ARM systems using FF-A v1.1 memory sharing.

Call-site confidence: medium. The patch shows the descriptor construction and bounds checks, but not all external callers.

## 4. Severity interpretation

This is not an ordinary low-risk correctness fix because the patch changes descriptor offset calculation and adds explicit bounds checks before writing into the transmit buffer. The realistic impact is likely malformed FF-A memory descriptors or denial of service in memory sharing operations. The theoretical risk is higher because descriptor corruption may affect memory access semantics between normal world, secure world, and endpoints.

There is not enough evidence for arbitrary write or reliable privilege escalation. The issue is best treated as Actionable Moderate with manual review, and as a weak Strong Important candidate only under the paranoid interpretation where local users can indirectly reach the FF-A memory sharing path.

## 5. One-sentence report phrase

An ARM FF-A descriptor offset bug can place Endpoint Memory Access Descriptor entries at the wrong location during memory sharing setup, causing malformed firmware-facing memory descriptors and possible local DoS or constrained descriptor corruption on FF-A v1.1 systems.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: the patch combines a spec-layout correction with new bounds checks around firmware-facing memory descriptors, which is enough to require manual review even though direct remote reachability and a proven LPE primitive are not shown.

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

Patch: firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation [ Upstream
Commit: b39b08e6bee812514b449dc874076890e6b871a0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b39b08e6bee812514b449dc874076890e6b871a0

Changed files:
  drivers/firmware/arm_ffa/driver.c
  include/linux/arm_ffa.h

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=b39b08e6bee812514b449dc874076890e6b871a0

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

The original Linux kernel CVE announcement for CVE-2026-68400 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68400

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:L/I:L/A:L
  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: 3
  Paranoid ActionableScore: 6

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).