[CVE-2026-74458][MODERATE 7.0] can: kvaser_usb_leaf: kvaser_usb_leaf_wait_cmd(): validate received command extents

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

CVE: CVE-2026-74458
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: kvaser_usb_leaf: kvaser_usb_leaf_wait_cmd(): validate received command extents
Commit: 695aea154bb2d453e6daada1510972fafd075285
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=695aea154bb2d453e6daada1510972fafd075285
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74458
Analysis date: Sat, 15 Aug 2026 17:48:55 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious or compromised Kvaser USB/CAN device can provide an oversized command length that causes `kvaser_usb_leaf_wait_cmd()` to copy device-controlled data past a fixed `struct kvaser_cmd`, leading to kernel memory corruption and possible DoS or privilege-escalation impact under physical or USB-device-control conditions.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74458 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74458

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-2026-74458	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:H/I:H/A:H';*CWE-787;CWE-130;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'A malicious or faulty Kvaser USB/CAN device can provide a variable length command with an invalid length field in the USB receive buffer. In kvaser_usb_leaf_wait_cmd(), a matching command was copied into a fixed struct kvaser_cmd using the device provided length, so an oversized command can cause an out-of-bounds write and corrupt kernel memory. For the CVSS the PR:N because no host privileges are required once the attacker can present or control the USB device. The issue is not network reachable and requires physical or equivalent USB device access. Impact is at least denial of service via kernel crash and may include privilege escalation because the primitive is a kernel memory overwrite from device controlled data. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	USB SIMPLEFIX ERRORPATH NETWORK HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Firmware-mediated external influence: +1
  The malformed command length and payload come from a USB CAN device or its firmware.

* Memory corruption, strong corruption primitive: +2
  `kvaser_usb_leaf_wait_cmd()` copied `tmp->len` bytes into a fixed `struct kvaser_cmd` without checking `sizeof(*cmd)`, creating a device-controlled out-of-bounds write.

* Weak to moderate LPE concern: +1 conservative, +2 paranoid
  The primitive is a kernel memory overwrite with device-controlled data, but target layout and exploit reliability are not demonstrated.

* Reliable kernel crash / strong DoS: +1
  Oversized copy or malformed command parsing can plausibly crash the kernel.

* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs in a trusted USB CAN kernel driver path parsing device-provided command buffers.

* Integrity impact plausible: +1
  Kernel memory overwrite can plausibly affect integrity, although no concrete privilege-escalation chain is shown.

Subtracted signals:

* Physical-only or rare hardware-only condition: -2
  Triggering requires a malicious, faulty, or compromised Kvaser USB/CAN device or equivalent USB-device control.

* Rare AND difficult-to-reach subsystem/configuration: -1
  Kvaser USB CAN is not a broad default attack surface compared with core networking or common filesystem paths.

## 3. Reachability analysis

The bug is triggerable by a malicious or faulty Kvaser USB/CAN device that returns malformed variable-length commands in the USB receive buffer. It is not network reachable. No host user privileges are required once the attacker can present or control the USB device, but realistic exploitation normally requires physical access, supply-chain compromise, malicious peripheral firmware, or a USB redirection scenario. Namespaces and containers do not materially lower the barrier because the vulnerable parsing happens in the host kernel USB driver.

Call-site confidence: high. The patch shows the vulnerable copy site and the added size check before `memcpy()`.

## 4. Severity interpretation

This is not an ordinary Moderate parser cleanup. The patch fixes a concrete out-of-bounds write into a fixed kernel structure using a device-provided length. Realistic exposure is limited by the physical or device-firmware attack requirement, so it does not look like a Strong Important issue by default. However, because the primitive is kernel memory corruption and not just a WARN or DoS-only condition, it should be treated as Actionable Moderate and should not be auto-closed without review.

## 5. One-sentence report phrase

A malicious or compromised Kvaser USB/CAN device can provide an oversized command length that causes `kvaser_usb_leaf_wait_cmd()` to copy device-controlled data past a fixed `struct kvaser_cmd`, leading to kernel memory corruption and possible DoS or privilege-escalation impact under physical or USB-device-control conditions.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a device-controlled kernel out-of-bounds write. Even though reachability is physical or firmware-mediated, the primitive is stronger than a simple crash or validation bug and may be exploitable depending on stack or heap layout at the affected call sites.

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

Patch: can: kvaser_usb_leaf: kvaser_usb_leaf_wait_cmd(): validate received command extents
Commit: 695aea154bb2d453e6daada1510972fafd075285
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=695aea154bb2d453e6daada1510972fafd075285

Commit description:

The wait and bulk receive paths walk variable-length commands from a
USB buffer. A nonzero command shorter than CMD_HEADER_LEN can still be
dispatched, and the wait path copies a matching command into a fixed
caller-owned struct kvaser_cmd using the device-provided length.

Reject nonzero commands that do not contain the fixed header or that
extend beyond the current USB buffer item. In the wait path, also reject
a matching command that exceeds the destination before copying it.

Fixes: 080f40a ("can: kvaser_usb: Add support for Kvaser CAN/USB devices")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260722042221.44066-1-pengpeng@iscas.ac.cn
Cc: stable@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/kvaser_usb/kvaser_usb_leaf.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=695aea154bb2d453e6daada1510972fafd075285

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

The original Linux kernel CVE announcement for CVE-2026-74458 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74458

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:R/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 4
  Paranoid ActionableScore: 5

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 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).