[CVE-2026-68401][MODERATE 7.0] firmware: arm_ffa: Fix out-of-bound writes in ffa_setup_and_transmit() [ Upstream

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

CVE: CVE-2026-68401
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: firmware: arm_ffa: Fix out-of-bound writes in ffa_setup_and_transmit() [ Upstream
Commit: cf5708c9d78c98214c62b1e5d049cd527a543b8e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf5708c9d78c98214c62b1e5d049cd527a543b8e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68401
Analysis date: Mon, 10 Aug 2026 11:52:28 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An out of bounds write in ARM FF-A `ffa_setup_and_transmit()` can corrupt descriptor or constituent data while building firmware memory transactions, causing at least local DoS risk and possible kernel memory corruption requiring manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68401 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68401

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-2026-68401	MODERATE	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:H/I:H/A:H';*CWE-787;CWE-131;CWE-119;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An out of bounds write in firmware arm_ffa ffa_setup_and_transmit can occur while building FF-A memory descriptors and fragment constituent entries. For FF-A versions below 1.2, the code could write reserved fields beyond the smaller endpoint memory access descriptor size. A second bounds check accepted a constituent pointer at the end of the Tx buffer without ensuring space for the full entry, so later writes could cross the buffer boundary. For the CVSS the PR:L is used because exploitation would normally require a local user or process that can reach an FF-A backed kernel service or device path, while systems without such exposure are less practically affected. The issue is not network reachable. Impact is at least local denial of service and data corruption risk due to kernel memory corruption, with possible privilege escalation requiring manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-68401 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WRITE OOB SIMPLEFIX LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Constrained kernel buffer overwrite: +1. The patch fixes explicit out of bound writes in `ffa_setup_and_transmit()`, but the overwritten data appears mostly fixed or kernel-derived inside an FF-A transmit buffer.
* Memory layout invariant restoration: +1. The fix restores consistency between FF-A version-dependent descriptor size, descriptor field layout, `max_fragsize`, and constituent entry size.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs in the ARM FF-A firmware driver, a trusted firmware communication path.
* Integrity impact plausible: +1. OOB writes can corrupt adjacent kernel or shared transmit-buffer state.
* Availability impact realistic: +1. Kernel memory corruption in this path can plausibly lead to crash or broken firmware transaction state.

Paranoid additional signals:

* Firmware-mediated external influence: +1. The vulnerable layout depends on FF-A firmware version and memory transaction formatting.
* Weak LPE concern: +1. OOB write in kernel context creates a theoretical privilege-escalation concern, but no attacker-controlled target, reclaim primitive, or arbitrary write is demonstrated.

Constraints / non-awarded signals:

* No Remote reachable / network-triggerable signal. This is not a network protocol path.
* No Strong LPE plausibility +2. The patch does not show controlled overwrite, object replacement, UAF reclaim, callback control, or arbitrary write.
* No Strong corruption primitive +2. The writes are constrained to descriptor/constituent construction in a firmware transmit buffer.

## 3. Reachability analysis

The likely trigger is a local process or kernel client that can cause FF-A memory sharing or related FF-A-backed service activity. Direct reachability by an ordinary unprivileged user depends on platform configuration and exposed client interfaces, such as trusted execution or firmware-backed services. Containers and namespaces do not automatically expose this path, but reduced-privilege service accounts or device-access policies could make it reachable without full host root.

The affected path is platform-specific and requires ARM FF-A support, so it is not universal across Linux deployments. However, where FF-A is enabled, the bug is in a privileged firmware communication path and the commit explicitly describes multiple out-of-bound writes. Call-site confidence: medium, because the changed function body and buffer construction logic are visible, but full userspace-to-FF-A call paths are not included in the supplied patch.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup because the patch fixes explicit OOB writes in kernel firmware code. Realistic impact is most clearly local DoS or firmware transaction corruption, and practical LPE is not demonstrated. The paranoid interpretation is still defensible as Strong Important candidate because kernel OOB writes in a trusted firmware path can corrupt adjacent state and require manual review, even if the primitive is constrained.

## 5. One-sentence report phrase

An out of bounds write in ARM FF-A `ffa_setup_and_transmit()` can corrupt descriptor or constituent data while building firmware memory transactions, causing at least local DoS risk and possible kernel memory corruption requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes multiple OOB writes in kernel code, and the exact severity depends on platform-specific FF-A exposure and whether any local FF-A-backed service allows attacker-controlled memory transaction shaping.

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UPSTREAM PATCH SUMMARY
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Patch: firmware: arm_ffa: Fix out-of-bound writes in ffa_setup_and_transmit() [ Upstream
Commit: cf5708c9d78c98214c62b1e5d049cd527a543b8e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf5708c9d78c98214c62b1e5d049cd527a543b8e

Changed files:
  drivers/firmware/arm_ffa/driver.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=cf5708c9d78c98214c62b1e5d049cd527a543b8e

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

The original Linux kernel CVE announcement for CVE-2026-68401 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68401

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:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 5
  Paranoid ActionableScore: 7

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).