[CVE-2026-74460][MODERATE REGULAR] can: ems_usb: validate CPC message lengths

[CVE-2026-74460][MODERATE REGULAR] can: ems_usb: validate CPC message lengths

[AL-KERNEL]

CVE: CVE-2026-74460
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: ems_usb: validate CPC message lengths
Commit: ce8125566b1d0b0f16449407e014addf451804ea
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ce8125566b1d0b0f16449407e014addf451804ea
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74460
Analysis date: Sat, 15 Aug 2026 15:25:56 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like with manual review due to kernel OOB read
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74460 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74460

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-2026-74460	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H';CWE-125;CWE-130;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.2';DESCR 'A malformed CPC message from an EMS CPC USB CAN adapter can be parsed without first proving that the declared message length fits inside the URB payload. The same receive path can also call CAN frame, CAN state, CAN error, or overrun handlers when the type-specific payload is shorter than the fields those handlers read. This creates an out-of-bounds read condition in the kernel USB receive callback. The issue is not network reachable over IP and normally requires a malicious or compromised USB CAN device, direct physical access to attach such a device, or an equivalent setup where the USB device side is attacker controlled. For the CVSS the PR:N is used because the attacker does not need an authenticated local account on the host once crafted CPC messages can be supplied by the USB device. Impact is at least denial of service via invalid kernel reads and possible kernel crash. A limited confidentiality impact is also defensible if stale bytes from the receive buffer are propagated into CAN frames visible to local consumers.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like with manual review due to kernel OOB read (with actual score 1)	YES	DANGER USB ERRORPATH NETWORK LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

### 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like with manual review due to kernel OOB read**

### 2. Signal breakdown

Conservative signals:

* Firmware-mediated or device-mediated external influence: +1
  The malformed input is supplied by the USB CAN device side, not by ordinary local userspace or the IP network.

* Reliable kernel crash / strong DoS: +1
  Missing length validation can make receive handlers read fields beyond the valid CPC message payload. This can plausibly crash the kernel depending on buffer layout.

* Physical-only or rare hardware-only condition: -2
  Practical triggering normally requires a malicious or compromised EMS CPC USB CAN adapter, physical access, or control over the USB device endpoint.

Conservative total: 0

Paranoid additional signal:

* Confidentiality impact plausible: +1
  A limited OOB read could potentially consume stale bytes from the receive buffer and propagate them into CAN-visible data paths, but no strong information disclosure primitive is demonstrated.

Paranoid total: 1

Not awarded:

* No remote/network-triggerable +2 because this is not reachable over IP or ordinary CAN network traffic without a malicious USB device endpoint.
* No generic strong memory corruption +2 because the patch shows bounds validation for reads, not OOB write, UAF, double free, type confusion, or controlled overwrite.
* No privilege escalation plausible +2 because there is no reclaim, write primitive, callback control, refcount abuse, or object replacement shown.

### 3. Reachability analysis

The likely attacker must control the USB device side of an EMS CPC USB CAN adapter or attach a malicious USB device that presents malformed CPC messages. A normal local unprivileged user cannot trigger this solely through syscalls unless they can influence the USB device firmware or physical device behavior. Containers and namespaces do not materially reduce the requirement, because the vulnerable input arrives from the USB hardware path. The driver is not a broad default remote attack surface and depends on specific CAN USB hardware being connected and active.

### 4. Severity interpretation

This behaves more like an ordinary Moderate / Low-like issue in practical deployment because exploitation is physical or device-mediated and the demonstrated primitive is a bounded receive-path validation failure leading mainly to OOB reads and possible crash. The theoretical memory-safety concern is real enough for manual review, but the patch does not support arbitrary write, UAF, privilege escalation, or remote network reachability.

### 5. One-sentence report phrase

Malformed CPC messages from an EMS CPC USB CAN device can bypass message length validation in ems_usb_read_bulk_callback and cause kernel out-of-bounds reads, with realistic impact limited mainly to physical or device-mediated DoS and possible limited information exposure.

### 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the score is low due to physical/device-mediated reachability, but the bug is still a kernel receive-path OOB read with a plausible crash and limited confidentiality concern, so it should not be blindly auto-closed without confirming actual data propagation and crash behavior.

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

Patch: can: ems_usb: validate CPC message lengths
Commit: ce8125566b1d0b0f16449407e014addf451804ea
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ce8125566b1d0b0f16449407e014addf451804ea

Commit description:

ems_usb_read_bulk_callback() walks CPC messages packed in one USB
receive buffer.

Check that each declared message fits in the URB payload. Also require the
type-specific payload to cover the fields used by the CAN, state, error and
overrun handlers.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260706092752.79600-1-pengpeng@iscas.ac.cn
Fixes: 702171a ("ems_usb: Added support for EMS CPC-USB/ARM7 CAN/USB interface")
Cc: stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/can/usb/ems_usb.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=ce8125566b1d0b0f16449407e014addf451804ea

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

The original Linux kernel CVE announcement for CVE-2026-74460 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74460

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:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.2

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: 0
  Paranoid ActionableScore: 1

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).