[CVE-2026-72115][MODERATE REGULAR] can: bcm: track a single source interface for ANYDEV timeout/throttle ops

[CVE-2026-72115][MODERATE REGULAR] can: bcm: track a single source interface for ANYDEV timeout/throttle ops

[AL-KERNEL]

CVE: CVE-2026-72115
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: bcm: track a single source interface for ANYDEV timeout/throttle ops
Commit: 18b45251e74e35668f0dd0c470549384ae191ecf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=18b45251e74e35668f0dd0c470549384ae191ecf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72115
Analysis date: Sat, 15 Aug 2026 22:13:15 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline Moderate / Manual review recommended
Manual review required: YES

Summary:
A race in CAN BCM ANYDEV receive operations with active timeout or throttle timers can let frames from multiple interfaces concurrently disturb timer handling and corrupt per-operation receive state, causing spurious RX_TIMEOUT notifications and local protocol-level DoS.

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

The original Linux kernel CVE announcement for CVE-2026-72115 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72115

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-72115	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:L/I:L/A:H';CWE-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'A race in CAN BCM ANYDEV receive operations can occur when one op with timeout/throttle timers receives matching frames from multiple CAN interfaces at the same time. bcm_rx_handler may then run concurrently on different CPUs for the same op and disturb timer handling around hrtimer_cancel and bcm_rx_timeout_handler. This can cause spurious RX_TIMEOUT notifications and corruption of shared per op state such as last_frames, rx_ifindex, and rx_stamp. For the CVSS the PR:L is used because a local user or local process must create and configure a CAN BCM receive operation, while extra privileges may only be needed to create CAN or vcan interfaces if they do not already exist. The issue is not directly reachable over IP networks, but CAN bus adjacent traffic can be part of the trigger when the local BCM operation is already configured. Impact is mainly denial of service and low integrity impact in delivered BCM state. 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 Borderline Moderate / Manual review recommended (with actual score 4)	YES	LOCK DANGER INIT SKB TIMER HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline Moderate / Manual review recommended**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  CAN BCM sockets and RX operations can typically be created by a local process if CAN support and interfaces are available.

* Local high-control kernel API refinement: +1
  BCM lets users configure receive ops, timers, throttling, multiplex frames, and ANYDEV matching. This gives meaningful control over kernel protocol state and timer behavior.

* Integrity impact plausible: +1
  The commit explicitly describes last_frames corruption and clobbering of rx_ifindex/rx_stamp, which can corrupt delivered BCM state and metadata.

* Availability impact realistic: +1
  Spurious RX_TIMEOUT notifications and disturbed watchdog/timer behavior can break userspace CAN consumers and cause protocol-level DoS for the affected BCM socket or application.

Negative or limiting signals:

* Hard or timing-dependent race: -1 in conservative score
  The issue requires concurrent matching frames from multiple CAN interfaces and a timeout/throttle configuration.

* Rare or configuration-dependent exposure: -1 in conservative score
  Practical triggering requires CAN BCM, ANYDEV rx ops, active timeout/throttle timers, and multiple CAN/vcan interfaces or multiple physical CAN sources.

Not awarded:

* No remote IP/network-triggerable score. CAN bus traffic can contribute, but this is not generally reachable over ordinary IP networking.
* No generic memory corruption score. The patch shows shared per-op state corruption, not UAF, OOB write, double-free, type confusion, or arbitrary write.
* No privilege escalation score. There is no demonstrated reclaim, callback control, refcount abuse, or write primitive.
* No strong kernel crash score. The commit describes spurious notifications and state corruption, not a reliable Oops or panic.

Call-site confidence: high. The relevant handler, setup path, and unregister notification path are included in the supplied patch.

## 3. Reachability analysis

A local process can configure a CAN BCM ANYDEV RX operation with timeout or throttle timers. The race requires matching CAN frames to arrive from more than one interface so that bcm_rx_handler() can execute concurrently for the same bcm_op on different CPUs. Creating vcan or physical CAN interfaces usually requires CAP_NET_ADMIN, but if such interfaces already exist, a less privileged local user may be able to use CAN sockets depending on system policy.

Namespaces can matter because CAP_NET_ADMIN in a network namespace may allow setup of vcan devices in some environments. However, this still remains a local/control-plane style trigger rather than a remotely reachable IP network bug. Physical CAN bus traffic may participate in triggering after the local BCM operation exists, but the patch does not support scoring it as generally remote reachable.

## 4. Severity interpretation

This behaves more like a borderline or actionable Moderate issue than an Important-class kernel vulnerability. The main evidence is a race in timer and per-op state handling, causing spurious timeout notifications and corruption of BCM-visible state. The theoretical concern is that races in network timer code deserve review, but the patch does not show memory lifetime corruption, attacker-controlled object reuse, stale callback dispatch, or an arbitrary write primitive.

Conservative handling can place it at the low end of manual review because the affected subsystem and configuration are specialized. Paranoid handling raises it slightly because CAN BCM exposes user-configurable timers and shared state, and the bug is a concurrency flaw in kernel networking code.

## 5. One-sentence report phrase

A race in CAN BCM ANYDEV receive operations with active timeout or throttle timers can let frames from multiple interfaces concurrently disturb timer handling and corrupt per-operation receive state, causing spurious RX_TIMEOUT notifications and local protocol-level DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not a proven memory-corruption or LPE issue, but it is a race in kernel networking timer handling with explicit shared-state corruption and local user-controlled BCM operation setup, so it should not be auto-closed without human review.

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

Patch: can: bcm: track a single source interface for ANYDEV timeout/throttle ops
Commit: 18b45251e74e35668f0dd0c470549384ae191ecf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=18b45251e74e35668f0dd0c470549384ae191ecf

Commit description:

An ANYDEV rx op (ifindex == 0) with an active RX timeout and/or
throttle timer has no defined semantics when matching frames arrive
from several interfaces: bcm_rx_handler() can run concurrently for
the same op on different CPUs, racing hrtimer_cancel()/
bcm_rx_starttimer() against bcm_rx_timeout_handler() and causing
spurious RX_TIMEOUT notifications and last_frames corruption. The
same concurrency lets throttled multiplex frames from different
interfaces clobber the single rx_ifindex/rx_stamp fields shared by
the op.

Add op->if_detected to track the first interface that delivers a
matching frame while a timeout/throttle timer is configured, and
reject frames from any other interface for that op. The claim is
decided in bcm_rx_handler() before hrtimer_cancel() touches
op->timer, so a rejected frame can never disturb the claimed
interface's watchdog. RTR-mode ops are excluded via RX_RTR_FRAME,
independent of kt_ival1/kt_ival2, since those may briefly hold a
stale value from an earlier non-RTR configuration.

The claim is released in bcm_notify() on NETDEV_UNREGISTER and in
bcm_rx_setup() when SETTIMER reconfigures the timer values.

A (re-)claim is only possible on CAN devices in NETREG_REGISTERED
dev->reg_state to cover the release in bcm_notify() where reg_state
becomes NETREG_UNREGISTERING until synchronize_net().

Fixes: ffd980f ("[CAN]: Add broadcast manager (bcm) protocol")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/linux-can/20260709105031.1A39C1F000E9@smtp.kernel.org/
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-11-562f7e3e42da@hartkopp.net
Cc: stable@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  net/can/bcm.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=18b45251e74e35668f0dd0c470549384ae191ecf

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

The original Linux kernel CVE announcement for CVE-2026-72115 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72115

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:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  Paranoid ActionableScore: 4

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).