[CVE-2026-74456][MODERATE 7.0] can: peak_usb: peak_usb_start(): fix double free of transfer buffer on URB submit error

[CVE-2026-74456][MODERATE 7.0] can: peak_usb: peak_usb_start(): fix double free of transfer buffer on URB submit error

[AL-KERNEL]

CVE: CVE-2026-74456
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: can: peak_usb: peak_usb_start(): fix double free of transfer buffer on URB submit error
Commit: 525640b93d3e5f82f4ebea4730f4e0cf799522ba
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=525640b93d3e5f82f4ebea4730f4e0cf799522ba
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74456
Analysis date: Sat, 15 Aug 2026 18:42:20 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A double-free in the PEAK USB CAN driver start error path can free the same RX URB transfer buffer via both kfree(buf) and usb_free_urb(), allowing a local privileged or delegated device-management context to crash the kernel and requiring manual review for possible heap-corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-74456 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74456

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-2026-74456	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-415;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A double-free can occur in the PEAK USB CAN driver error path when peak_usb_start() allocates an RX transfer buffer and sets URB_FREE_BUFFER on the URB. If usb_submit_urb() fails, the old error path frees the buffer with kfree(buf) and then calls usb_free_urb(), which frees the same transfer buffer again because URB_FREE_BUFFER is set. This is a local memory corruption issue and can at least crash the kernel. For the CVSS the PR:L is used for the paranoid score because a reduced capability root, container root, service account, or delegated CAP_NET_ADMIN process may be able to start or reset the CAN network interface without being full host root. The issue is not network reachable in the IP sense and requires local control over the affected USB CAN device or its network interface. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to double-free memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	DANGER USB ERRORPATH UAF NETWORK LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	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: **Strong Important candidate / Actionable Moderate at minimum**::

Selected interpretation: **Actionable Moderate at minimum**, not a clear Strong Important candidate, because the bug is real kernel memory corruption but the trigger is local, device-dependent, and tied to an URB submit error path.

## 2. Signal breakdown

Triggered signals:

* Generic memory corruption, strong primitive: +2
  The patch fixes a confirmed double-free of a kmalloc() transfer buffer.

* Real lifetime corruption: +1
  The same buffer lifetime is owned both by explicit kfree(buf) and by usb_free_urb() via URB_FREE_BUFFER.

* Reliable kernel crash / strong DoS: +1
  KASAN reports a double-free in usb_free_urb(), and this can crash the kernel depending on allocator and panic settings.

* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs in a USB CAN network driver start/error path involving URB ownership and transfer buffer lifetime.

* Availability impact realistic: +1
  A successful trigger can cause a host kernel crash, not merely a recoverable warning.

Negative signals:

* Hard or unreliable trigger / special error path: -1
  The double-free requires usb_submit_urb() failure during peak_usb_start(), not ordinary packet traffic.

* Requires CAP_NET_ADMIN or equivalent device control in typical deployments: -1
  Starting or resetting the CAN network interface usually requires administrative network privileges, but delegated CAP_NET_ADMIN, service accounts, or container root can make this less than full host-root.

* Rare / hardware-specific exposure: -1
  The issue requires an affected PEAK USB CAN adapter and the peak_usb driver path.

Paranoid-only signal:

* Weak LPE concern: +1
  Double-free is a real memory corruption primitive, but the patch does not show attacker-controlled reclaim, replacement object control, callback control, or an arbitrary write. This justifies manual review but not automatic Important classification.

## 3. Reachability analysis

The bug is locally triggerable by a user or process that can bring up or otherwise control the affected PEAK USB CAN network device and cause the URB submit error path. In normal deployments this usually requires CAP_NET_ADMIN, root, or a privileged device-management service.

Namespaces and containers may lower the practical privilege requirement if the CAN netdev or CAP_NET_ADMIN is delegated into a container or service context. This should not be treated as a remote IP-network vulnerability. The attack requires local access to the affected USB CAN device or to a management path that can operate it.

The path is not broadly default-exposed. It depends on specific hardware and driver use, but the bug class is stronger than a pure DoS because the primitive is a confirmed double-free.

Call-site confidence: high. The patch and commit message show the allocation, URB_FREE_BUFFER ownership rule, explicit kfree(buf), and subsequent usb_free_urb() call in the same error path.

## 4. Severity interpretation

This behaves as an **actionable Moderate** issue with memory-corruption significance. The realistic impact is local kernel crash / DoS under device-specific conditions. The theoretical risk is higher because double-free bugs can sometimes be shaped into more serious heap corruption, but the provided patch does not demonstrate reclaim control, type confusion, callback control, or arbitrary write.

Therefore it should not be auto-closed as an ordinary low-priority Moderate, but it also does not have enough evidence for a strong Important classification without manual confirmation.

## 5. One-sentence report phrase

A double-free in the PEAK USB CAN driver start error path can free the same RX URB transfer buffer via both kfree(buf) and usb_free_urb(), allowing a local privileged or delegated device-management context to crash the kernel and requiring manual review for possible heap-corruption impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is confirmed double-free memory corruption in kernel driver code. Although practical triggering is local and hardware/error-path dependent, the primitive is strong enough that allocator behavior, reclaim control, and delegated CAP_NET_ADMIN/container exposure should be checked manually.

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

Patch: can: peak_usb: peak_usb_start(): fix double free of transfer buffer on URB submit error
Commit: 525640b93d3e5f82f4ebea4730f4e0cf799522ba
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=525640b93d3e5f82f4ebea4730f4e0cf799522ba

Commit description:

In peak_usb_start(), each RX URB transfer buffer is allocated with kmalloc()
and the URB is flagged URB_FREE_BUFFER so that the final usb_free_urb() also
frees the transfer buffer.

If usb_submit_urb() fails, the error path frees the buffer explicitly with
kfree(buf) and then calls usb_free_urb(urb). Because URB_FREE_BUFFER is set,
usb_free_urb() -> urb_destroy() frees the same buffer a second time, a double
free of the transfer buffer.

  BUG: KASAN: double-free in usb_free_urb.part.0+0x91/0xb0
  Free of addr ffff8881069ccb80 by task trigger.sh/285

  Call Trace:
   kfree+0x113/0x3c0
   usb_free_urb.part.0+0x91/0xb0

Drop the redundant kfree(buf); usb_free_urb() already releases the transfer
buffer. This mirrors commit 03819ab ("net: usb: lan78xx: Fix double free
issue with interrupt buffer allocation").

Fixes: bb47855 ("can: usb: PEAK-System Technik USB adapters driver core")
Closes: https://lore.kernel.org/linux-can/178159320216.2154888.16953451793788581739@maoyixie.com/T/#u
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Vincent Mailhol <mailhol@kernel.org>
Link: https://patch.msgid.link/178163373110.2507866.216458825145756798@maoyixie.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/can/usb/peak_usb/pcan_usb_core.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=525640b93d3e5f82f4ebea4730f4e0cf799522ba

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

The original Linux kernel CVE announcement for CVE-2026-74456 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74456

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:H
  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: 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: 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).